Poly(vinyl acetal) resin compositions, layers, and interlayers having enhanced optical properties

ABSTRACT

A tapered interlayer comprising at least one resin layer and a having tapered zone with a wedge angle of at least 0.13 mrad. The first resin layer comprises a first poly(vinyl acetal) resin and at least one RI balancing agent. The refractive index of the first resin layer is at least 1.480.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.14/563,011, filed Dec. 8, 2014, the contents of which is incorporatedherein by reference in its entirety.

BACKGROUND 1. Field of the Invention

This disclosure relates to polymer resins and, in particular, to polymerresins suitable for use in polymer interlayers, including those utilizedin multiple layer panels.

2. Description of Related Art

Poly(vinyl butyral) (PVB) is often used in the manufacture of polymersheets that can be used as interlayers in multiple layer panels,including, for example, light-transmitting laminates such as safetyglass or polymeric laminates. PVB is also used in photovoltaic solarpanels to encapsulate the panels which are used to generate and supplyelectricity for commercial and residential applications.

Safety glass generally refers to a transparent laminate that includes atleast one polymer sheet, or interlayer, disposed between two sheets ofglass. Safety glass is often used as a transparent barrier inarchitectural and automotive applications, and one of its primaryfunctions is to absorb energy resulting from impact or a blow withoutallowing penetration of the object through the glass and to keep theglass bonded even when the applied force is sufficient to break theglass. This prevents dispersion of sharp glass shards, which minimizesinjury and damage to people or objects within an enclosed area. Safetyglass may also provide other benefits, such as a reduction inultraviolet (UV) and/or infrared (IR) radiation, and it may also enhancethe aesthetic appearance of window openings through addition of color,texture, and the like. Additionally, safety glass with desirableacoustic properties has also been produced, which results in quieterinternal spaces.

Often, polymers that exhibit one set of desirable properties, such asacoustic performance, lack other desirable properties, such as impactresistance or strength. Therefore, in order to achieve desirablecombinations of properties, multilayered polymer interlayers have beenused. These multilayered interlayers may include at least one inner“core” layer sandwiched between two outer “skin” layers. Often, the corelayer of an interlayer may be a softer layer having a lower glasstransition temperature, which enhances its acoustic performance.However, because such resin layers can be difficult to easily processand/or transport, the skin layers of such multilayered interlayers areoften stiffer, with higher glass transition temperatures, which impartsenhanced processability, strength, and impact resistance to theinterlayer.

However, use of various layers having different properties can alsoproduce optical defects within the interlayer. For example, one defectcommon to these types of multilayer interlayers is mottle. Mottle is anobjectionable form of optical distortion or visual defect appearing asuneven spots or texture, usually in the final structure. Mottle iscaused by small-scale surface variations at the interfaces between thesoft and stiff layers wherein the individual layers have differentrefractive indices. Clarity is another important optical property thatis determined by measuring the level of haze within the interlayer orpanel. High haze typically occurs when different types of opticallyincompatible polymers and/or plasticizers are blended or mixed together.In such mixtures, light passing through the blend is scattered as itencounters regions of different polymer materials, and the result is ahazy, visually unclear appearance. High clarity polymers and interlayersare those having very low haze values.

Thus, a need exists for polymer resins, resin layers, and interlayersthat exhibit desirable optical properties, such as reduced haze andmottle and improved clarity, without sacrificing other properties,including impact resistance and acoustic performance. Such interlayerscould be monolithic or multilayered and should be usable in a widevariety of applications, including safety glass and polymer laminates.

SUMMARY

One embodiment of the present invention concerns a tapered interlayercomprising a first resin layer comprising a first poly(vinyl acetal)resin and at least one RI balancing agent. The refractive index of thefirst resin layer is at least 1.480 and the interlayer comprises atapered zone having a wedge angle of at least 0.13 mrad.

Another embodiment of the present invention relates to a taperedinterlayer comprising a first resin layer comprising a first poly(vinylacetal) resin and a second resin layer comprising a second poly(vinylacetal) resin. The first and second resin layers are adjacent to oneanother. At least one of said first and second poly(vinyl acetal) resinscomprises at least one RI balancing agent. The absolute value of thedifference between the refractive index of said first resin layer andthe refractive index of said second resin layer is less than 0.010. Thetapered interlayer comprises a tapered zone having a wedge angle of atleast 0.13 mrad.

Still another embodiment of the present invention concerns a taperedinterlayer comprising a first resin layer comprising a first poly(vinylacetal) resin and at least one RI balancing agent, wherein therefractive index of said first resin layer is at least 1.480, andwherein said interlayer comprises at least one constant angle taperedzone having a constant wedge angle of at least 0.13 mrad.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the present invention are described in detailbelow with reference to the attached drawing Figures, wherein:

FIG. 1 is a cross-sectional view of a tapered interlayer configured inaccordance with one embodiment of the present invention, where variousfeatures of the tapered interlayer are labeled for ease of reference;

FIG. 2 is a cross-sectional view of a tapered interlayer having atapered zone that extends over the entire width of the interlayer, wherethe entire tapered zone has a constant wedge angle and a linearthickness profile;

FIG. 3 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer and aflat edge zone that extends over part of the width of the interlayer,where the tapered zone includes a constant angle zone and a variableangle zone;

FIG. 4 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone includes a constant angle zone andtwo variable angle zones;

FIG. 5 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone is formed entirely of a variableangle zones having a curved thickness profile;

FIG. 6 is a cross-sectional view of a tapered interlayer having atapered zone that extends over the entire width of the interlayer, wherethe tapered includes three constant angle zones spaced from one anotherby two variable angle zones;

FIG. 7 is a cross-sectional view of a tapered interlayer having atapered zone that extends over part of the width of the interlayer andtwo flat edge zones that extend over part of the width of theinterlayer, where the tapered zone includes three constant angle zoneand four variable angle zones;

FIG. 8a is a plan view of a tapered interlayer configured for use in avehicle windshield, where the thickness provide of the interlayer issimilar to the thickness profile of the interlayer depicted in FIG. 2;and

FIG. 8b is a cross-sectional view of the interlayer of FIG. 8a , showingthe thickness profile of the interlayer.

DETAILED DESCRIPTION

Resin compositions, layers, and interlayers according to variousembodiments of the present invention can comprise one or morethermoplastic polymers and a refractive index (RI) balancing agent. Asused herein, the term “refractive index balancing agent” or “RIbalancing agent” refers to any component or additive included in thecomposition, layer, or interlayer for adjusting the refractive index ofat least one of the resins or layers. The RI balancing agent mayincrease or reduce the refractive index of at least one of the resins orlayers within an interlayer, which may improve the optical properties ofthe interlayer, including mottle, haze, and/or clarity, as compared toan identical interlayer formed without an RI balancing agent.

As used herein, the terms “polymer resin composition” and “resincomposition” refer to compositions including one or more polymer resins.Polymer compositions may optionally include other components, such asplasticizers and/or other additives. As used herein, the terms “polymerresin layer” and “resin layer” refer to one or more polymer resins,optionally combined with one or more plasticizers, that have been formedinto a polymeric sheet. Again, resin layers can include additionaladditives, although these are not required. As used herein, the term“interlayer” refers to a single or multiple layer polymer sheet suitablefor use with at least one rigid substrate to form a multiple layerpanel. The terms “single-sheet” interlayer and “monolithic” interlayerrefer to interlayers formed of one single resin sheet, while the terms“multiple layer” and “multilayer” interlayer refer to interlayers havingtwo or more resin sheets coextruded, laminated, or otherwise coupled toone another.

The resin compositions, layers, and interlayers described herein mayinclude one or more thermoplastic polymers. Examples of suitablethermoplastic polymers can include, but are not limited to, poly(vinylacetal) resins, polyurethanes (PU), poly(ethylene-co-vinyl) acetates(EVA), polyvinyl chlorides (PVC), poly(vinylchloride-co-methacrylate),polyethylenes, polyolefins, ethylene acrylate ester copolymers,poly(ethylene-co-butyl acrylate), silicone elastomers, epoxy resins, andacid copolymers such as ethylene/carboxylic acid copoloymers andionomers thereof, derived from any of the previously-listed polymers,and combinations thereof. In some embodiments, the thermoplastic polymercan be selected from the group consisting of poly(vinyl acetal) resins,polyvinyl chloride, and polyurethanes, or the resin can comprise one ormore poly(vinyl acetal) resins. Although described herein with respectto poly(vinyl acetal) resins, it should be understood that one or moreof the above polymer resins could be included with, or in the place of,the poly(vinyl acetal) resins described below in accordance with variousembodiments of the present invention.

When the resin compositions, layers, and interlayers described hereininclude poly(vinyl acetal) resins, the poly(vinyl acetal) resins can beformed according to any suitable method. Poly(vinyl acetal) resins canbe formed by acetalization of polyvinyl alcohol with one or morealdehydes in the presence of an acid catalyst. The resulting resin canthen be separated, stabilized, and dried according to known methods suchas, for example, those described in U.S. Pat. Nos. 2,282,057 and2,282,026, as well as “Vinyl Acetal Polymers,” in the Encyclopedia ofPolymer Science & Technology, 3^(rd) ed., Volume 8, pages 381-399, by B.E. Wade (2003). The resulting poly(vinyl acetal) resins may have a totalpercent acetalization of at least about 50, at least about 60, at leastabout 70, at least about 75, at least about 80, at least about 85 weightpercent, measured according to ASTM D-1396, unless otherwise noted. Thetotal amount of aldehyde residues in a poly(vinyl acetal) resin can becollectively referred to as the acetal component, with the balance ofthe poly(vinyl acetal) resin being residual hydroxyl and residualacetate groups, which will be discussed in further detail below.

According to some embodiments, the resin composition, layer, orinterlayer may include at least one poly(vinyl acetal) resin, which maybe present in the composition, layer, or interlayer in an amount of atleast about 0.5, at least about 1, at least about 2, at least about 3,at least about 5, at least about 10, at least about 15, at least about20, at least about 30, at least about 40, or at least about 45 weightpercent, based on the combined weight of all resins in the composition,layer, or interlayer. Together, the at least one poly(vinyl acetal)resins can make up at least about 10, at least about 20, at least about30, at least about 40, at least about 50, at least about 60, at leastabout 70, or at least about 80 weight percent of composition, layer, orinterlayer, based on the combined weight of all resins. In someembodiments, the amount of resins other than the at least one poly(vinylacetal) resin can be not more than about 20, not more than about 15, notmore than about 10, not more than about 5, not more than about 2, or notmore than about 1 weight percent, based on the combined weight of allresins.

In some embodiments, the resin composition, layer, or interlayer caninclude at least a first poly(vinyl acetal) resin and a secondpoly(vinyl acetal) resin, each of which may be present in thecomposition, layer, or interlayer in an amount of at least about 0.5, atleast about 1, at least about 2, at least about 3, at least about 5, atleast about 10, at least about 15, at least about 20, at least about 30,at least about 40, or at least about 45 weight percent, based on thecombined weight of all resins in the composition, layer, or interlayer.Together, the first and second poly(vinyl acetal) resins can make up atleast about 10, at least about 20, at least about 30, at least about 40,at least about 50, at least about 60, at least about 70, or at leastabout 80 weight percent of composition, layer, or interlayer, based onthe combined weight of all resins. In some embodiments, the amount ofresins other than the first and second poly(vinyl acetal) resins can benot more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 2, or not more than about 1weight percent, based on the combined weight of all resins.

In some embodiments, one of the first and the second poly(vinyl acetal)resins can be present in the composition, layer, or interlayer in anamount of less than 12 weight percent, based on the combined weight ofthe first and second poly(vinyl acetal) resins. For example, the firstor the second poly(vinyl acetal) resin can be present in thecomposition, layer, or interlayer in an amount of at least about 0.5, atleast about 1, at least about 1.5, at least about 2, at least about 2.5,at least about 3, at least about 3.5, at least about 4, at least about4.5, at least about 5, at least about 5.5, at least about 6, at leastabout 6.5, at least about 7 weight percent and/or not more than about12, not more than about 11.5, not more than about 11, not more thanabout 10.5, not more than about 10, not more than about 9.5, not morethan about 9, not more than about 8.5, not more than about 8, not morethan about 7.5 weight percent, based on the combined weight of the firstand second poly(vinyl acetal) resins. In some embodiments, one of thefirst and second poly(vinyl acetal) resins can be present in thecomposition, layer, or interlayer in an amount in the range of fromabout 0.5 to about 12, about 1.5 to about 11.5, about 2 to about 11,about 2.5 to about 10 weight percent, based on the combined weight ofthe first and second poly(vinyl acetal) resins.

The first and second poly(vinyl acetal) resins can include residues ofany suitable aldehyde and, in some embodiments, can include residues ofat least one C₁ to C₁₀ aldehyde, at least one C₄ to C₈ aldehyde.Examples of suitable C₄ to C₈ aldehydes can include, but are not limitedto, n-butyraldehyde, iso-butyraldehyde, 2-methylvaleraldehyde, n-hexylaldehyde, 2-ethylhexyl aldehyde, n-octyl aldehyde, and combinationsthereof. At least one of the first and second poly(vinyl acetal) resinscan include at least about 20, at least about 30, at least about 40, atleast about 50, at least about 60, or at least about 70 weight percentof residues of at least one C₄ to C₈ aldehyde, based on the total weightof aldehyde residues of the resin, and/or can include not more thanabout 90, not more than about 85, not more than about 80, not more thanabout 75, not more than about 70, or not more than about 65 weightpercent of at least one C₄ to C₈ aldehyde, or in the range of from about20 to about 90, about 30 to about 80, or about 40 to about 70 weightpercent of at least one C₄ to C₈ aldehyde. The C₄ to C₈ aldehyde may beselected from the group listed above, or it can be selected from thegroup consisting of n-butyraldehyde, iso-butyraldehyde, 2-ethylhexylaldehyde, and combinations thereof.

In various embodiments, the first and/or second poly(vinyl acetal) resinmay be a polyvinyl n-butyral (PVB) resin. In other embodiments, thefirst and/or second poly(vinyl acetal) resin can be a poly(vinyln-butyral) resin that mainly comprises residues of n-butyraldehyde, andmay, for example, include not more than about 50, not more than about40, not more than about 30, not more than about 20, not more than about10, not more than about 5, or not more than about 2 weight percent ofresidues of an aldehyde other than n-butyraldehyde, based on the totalweight of all aldehyde residues of the resin. When the first and/orsecond poly(vinyl acetal) resins are PVB resins, the molecular weight ofthe resins can be at least about 50,000, at least about 70,000, at leastabout 100,000 Daltons and/or not more than about 600,000, not more thanabout 550,000, not more than about 500,000, not more than about 450,000,or not more than 425,000 Daltons, measured by size exclusionchromatography using low angle laser light scattering (SEC/LALLS) methodof Cotts and Ouano. As used herein, the term “molecular weight” refersto weight average molecular weight (Mw). The molecular weight of thefirst and/or second poly(vinyl acetal) resin can be in the range of fromabout 50,000 to about 600,000, about 70,000 to about 450,000, or about100,000 to about 425,000 Daltons.

Although generally described herein with respect to first and secondpoly(vinyl acetal) resins, it should be understood that, in someembodiments, an equivalent single poly(vinyl acetal) resin includingfirst and second acetal moieties may be substituted for the first andsecond poly(vinyl acetal) resins with similar results. As used herein,the term “poly(vinyl acetal) resin component” can refer to an individualpoly(vinyl acetal) resin present in a blend of resins or to an acetalmoiety present on a single poly(vinyl acetal) resin. In variousembodiments, the ratio, by weight, of the amount of the first poly(vinylacetal) resin component to the second poly(vinyl acetal) resin componentin a layer, interlayer, or blend can be in the range of from about0.5:99.5 to about 99.5:0.5, about 1:99 to 99:1, about 10:90 to about90:10, about 25:75 to about 75:25, or about 40:60 to about 60:40.

In some embodiments, at least one resin composition, layer, orinterlayer can include at least a first poly(vinyl acetal) resincomponent and a second poly(vinyl acetal) resin component. In someembodiments, the first and second resin components may comprise firstand second poly(vinyl acetal) resins that can be physically mixed toform a resin blend, which may be combined with one or more plasticizersor other additives to provide a blended resin layer or interlayer. Inother embodiments, the first and second poly(vinyl acetal) resincomponents may be present as respective first and second acetal moietiesin a single poly(vinyl acetal) resin. As with the resin blend, thissingle “hybrid” poly(vinyl acetal) resin can be optionally blended witha plasticizer and utilized in resin layers and interlayers.

In some embodiments, when the resin components include poly(vinylacetal) resins, the first and second poly(vinyl acetal) resins may beblended such that one of the first and second resins is dispersed withinthe other of the first and second resins, which can form domains of oneof the first and second poly(vinyl acetal) resins within the other ofthe first and second poly(vinyl acetal) resins. Such a blended resin maybe used as a single layer interlayer or it may be combined with one ormore adjacent layers to form a multilayer interlayer. In otherembodiments, the first and second poly(vinyl acetal) resins can bepresent in adjacent layers of a multilayer interlayer, such that one ofthe layers of the interlayer includes the first poly(vinyl acetal) resinand another layer of the interlayer includes the second poly(vinylacetal) resin. Additional layers can also be present adjacent to atleast one of the layers.

The resin compositions, layers, and interlayers according to variousembodiments of the present invention can further include at least oneplasticizer. Depending on the specific composition of the resin orresins in a composition, layer, or interlayer, the plasticizer may bepresent in an amount of at least about 5, at least about 10, at leastabout 15, at least about 20, at least about 25, at least about 30, atleast about 35, at least about 40, at least about 45, at least about 50,at least about 55, at least about 60 parts per hundred parts of resin(phr) and/or not more than about 120, not more than about 110, not morethan about 105, not more than about 100, not more than about 95, notmore than about 90, not more than about 85, not more than about 75, notmore than about 70, not more than about 65, not more than about 60, notmore than about 55, not more than about 50, not more than about 45, ornot more than about 40 phr, or in the range of from about 5 to about120, about 10 to about 110, about 20 to about 90, or about 25 to about75 phr. Specific embodiments are discussed in detail shortly.

As used herein, the term “parts per hundred parts of resin” or “phr”refers to the amount of plasticizer present as compared to one hundredparts of resin, on a weight basis. For example, if 30 grams ofplasticizer were added to 100 grams of a resin, the plasticizer would bepresent in an amount of 30 phr. If the resin composition, layer, orinterlayer includes two or more resins, the weight of plasticizer iscompared to the combined amount of all resins present to determine theparts per hundred resin. Further, when the plasticizer content of alayer or interlayer is provided herein, it is provided with reference tothe amount of plasticizer in the mix or melt that was used to producethe layer or interlayer.

Examples of suitable plasticizers can include, but are not limited to,triethylene glycol di-(2-ethylhexanoate) (“3GEH”), triethylene glycoldi-(2-ethylbutyrate), triethylene glycol diheptanoate, tetraethyleneglycol diheptanoate, tetraethylene glycol di-(2-ethylhexanoate)(“4GEH”), dihexyl adipate, dioctyl adipate, hexyl cyclohexyladipate,diisononyl adipate, heptylnonyl adipate, di(butoxyethyl) adipate, andbis(2-(2-butoxyethoxy)ethyl) adipate, dibutyl sebacate, dioctylsebacate, and mixtures thereof. The plasticizer may be selected from thegroup consisting of triethylene glycol di-(2-ethylhexanoate) andtetraethylene glycol di-(2-ethylhexanoate), or the plasticizer cancomprise triethylene glycol di-(2-ethylhexanoate).

According to some embodiments, the first and second poly(vinyl acetal)resins in the compositions, layers, and interlayers described herein canhave different compositions. For example, in some embodiments, the firstpoly(vinyl acetal) resin can have a residual hydroxyl content and/orresidual acetate content that is at least about 2, at least about 3, atleast about 4, at least about 5, at least about 6, or at least about 8weight percent higher or lower than the residual hydroxyl content and/orresidual acetate content of the second poly(vinyl acetal) resin. As usedherein, the terms “residual hydroxyl content” and “residual acetatecontent” refer to the amount of hydroxyl and acetate groups,respectively, that remain on a resin after processing is complete. Forexample, polyvinyl n-butyral can be produced by hydrolyzing polyvinylacetate to polyvinyl alcohol, and then acetalizing the polyvinyl alcoholwith n-butyraldehyde to form polyvinyl n-butyral. In the process ofhydrolyzing the polyvinyl acetate, not all of the acetate groups areconverted to hydroxyl groups, and residual acetate groups remain on theresin. Similarly, in the process of acetalizing the polyvinyl alcohol,not all of the hydroxyl groups are converted to acetal groups, whichalso leaves residual hydroxyl groups on the resin. As a result, mostpoly(vinyl acetal) resins include both residual hydroxyl groups (asvinyl hydroxyl groups) and residual acetate groups (as vinyl acetategroups) as part of the polymer chain. The residual hydroxyl content andresidual acetate content are expressed in weight percent, based on theweight of the polymer resin, and are measured according to ASTM D-1396,unless otherwise noted.

The difference between the residual hydroxyl content of the first andsecond poly(vinyl acetal) resins could also be at least about 2, atleast about 5, at least about 10, at least about 12, at least about 15,at least about 20, or at least about 30 weight percent. As used herein,the term “weight percent different” or “the difference is at leastweight percent” refers to a difference between two given weightpercentages, calculated by subtracting the one number from the other.For example, a poly(vinyl acetal) resin having a residual hydroxylcontent of 12 weight percent has a residual hydroxyl content that is 2weight percent lower than a poly(vinyl acetal) resin having a residualhydroxyl content of 14 weight percent (14 weight percent−12 weightpercent=2 weight percent). As used herein, the term “different” canrefer to a value that is higher than or lower than another value.

At least one of the first and second poly(vinyl acetal) resins can havea residual hydroxyl content of at least about 14, at least about 14.5,at least about 15, at least about 15.5, at least about 16, at leastabout 16.5, at least about 17, at least about 17.5, at least about 18,at least about 18.5, at least about 19, at least about 19.5 and/or notmore than about 45, not more than about 40, not more than about 35, notmore than about 33, not more than about 30, not more than about 27, notmore than about 25, not more than about 22, not more than about 21.5,not more than about 21, not more than about 20.5, or not more than about20 weight percent, or in the range of from about 14 to about 45, about16 to about 30, about 18 to about 25, about 18.5 to about 20, or about19.5 to about 21 weight percent.

The other poly(vinyl acetal) resin can have a residual hydroxyl contentof at least about 8, at least about 9, at least about 10, at least about11 weight percent and/or not more than about 16, not more than about 15,not more than about 14.5, not more than about 13, not more than about11.5, not more than about 11, not more than about 10.5, not more thanabout 10, not more than about 9.5, or not more than about 9 weightpercent, or in the range of from about 8 to about 16, about 9 to about15, or about 9.5 to about 14.5 weight percent, and can be selected suchthat the difference between the residual hydroxyl content of the firstand second poly(vinyl acetal) resin is at least about 2 weight percent,as mentioned previously. One or more other poly(vinyl acetal) resins mayalso be present in the resin composition, layer, or interlayer and canhave a residual hydroxyl within the ranges provided above. Additionally,the residual hydroxyl content of the one or more other poly(vinylacetal) resins can be the same as or different than the residualhydroxyl content of the first and/or second poly(vinyl acetal) resins.

In some embodiments, at least one of the first and second poly(vinylacetal) resins can have a residual acetate content different than theother. For example, in some embodiments, the difference between theresidual acetate content of the first and second poly(vinyl acetal)resins can be at least about 2, at least about 3, at least about 4, atleast about 5, at least about 8, at least about 10 weight percent. Oneof the poly(vinyl acetal) resins may have a residual acetate content ofnot more than about 4, not more than about 3, not more than about 2, ornot more than about 1 weight percent, measured as described above. Insome embodiments, at least one of the first and second poly(vinylacetal) resins can have a residual acetate content of at least about 5,at least about 8, at least about 10, at least about 12, at least about14, at least about 16, at least about 18, at least about 20, or at leastabout 30 weight percent. The difference in the residual acetate contentbetween the first and second poly(vinyl acetal) resins can be within theranges provided above, or the difference can be less than about 3, notmore than about 2, not more than about 1, or not more than about 0.5weight percent. Additional poly(vinyl acetal) resins present in theresin composition or interlayer can have a residual acetate content thesame as or different than the residual acetate content of the firstand/or second poly(vinyl acetal) resin.

In some embodiments, the difference between the residual hydroxylcontent of the first and second poly(vinyl acetal) resins can be lessthan about 2, not more than about 1, not more than about 0.5 weightpercent and the difference in the residual acetate content between thefirst and second poly(vinyl acetal) resins can be at least about 3, atleast about 5, at least about 8, at least about 15, at least about 20,or at least about 30 weight percent. In other embodiments, thedifference in the residual acetate content of the first and secondpoly(vinyl acetal) resins can be less than about 3, not more than about2, not more than about 1, or not more than about 0.5 weight percent andthe difference in the residual hydroxyl content of the first and secondpoly(vinyl acetal) resins can be at least about 2, at least about 5, atleast about 10, at least about 12, at least about 15, at least about 20,or at least about 30 weight percent.

In various embodiments, the differences in residual hydroxyl and/orresidual acetate content of the first and second poly(vinyl acetal)resins can be selected to control or provide certain performanceproperties, such as strength, impact resistance, penetration resistance,processability, or acoustic performance to the final composition, layer,or interlayer. For example, poly(vinyl acetal) resins having a higherresidual hydroxyl content, usually greater than about 16 weight percent,can facilitate high impact resistance, penetration resistance, andstrength to a resin composition or layer, while lower hydroxyl contentresins, usually having a residual hydroxyl content of less than 16weight percent, can improve the acoustic performance of the interlayeror blend.

Poly(vinyl acetal) resins having higher or lower residual hydroxylcontents and/or residual acetate contents may also, when combined withat least one plasticizer, ultimately include different amounts ofplasticizer. As a result, layers or domains formed of first and secondpoly(vinyl acetal) resins having different compositions may also havedifferent properties within a single resin layer or interlayer. Althoughnot wishing to be bound by theory, it is assumed that the compatibilityof a given plasticizer with a poly(vinyl acetal) resin can depend, atleast in part, on the composition of the polymer, and, in particular, onits residual hydroxyl content. Overall, poly(vinyl acetal) resins withhigher residual hydroxyl contents tend to exhibit a lower compatibility(or capacity) for a given plasticizer as compared to similar resinshaving a lower residual hydroxyl content. As a result, poly(vinylacetal) resins with higher residual hydroxyl contents tend to be lessplasticized and exhibit higher stiffness than similar resins havinglower residual hydroxyl contents. Conversely, poly(vinyl acetal) resinshaving lower residual hydroxyl contents may tend to, when plasticizedwith a given plasticizer, incorporate higher amounts of plasticizer,which may result in a softer resin layer that exhibits a lower glasstransition temperature than a similar resin having a higher residualhydroxyl content. Depending on the specific resin and plasticizer, thesetrends could be reversed.

When two poly(vinyl acetal) resins having different levels of residualhydroxyl content are blended with a plasticizer, the plasticizer maypartition between the resin layers or domains, such that moreplasticizer can be present in the layer or domain having the lowerresidual hydroxyl content and less plasticizer may be present in thelayer or domain having the higher residual hydroxyl content. Ultimately,a state of equilibrium is achieved between the two resins. Thecorrelation between the residual hydroxyl content of a poly(vinylacetal) resin and plasticizer compatibility/capacity can facilitateaddition of a proper amount of plasticizer to the polymer resin. Such acorrelation also helps to stably maintain the difference in plasticizercontent between two or more resins when the plasticizer would otherwisemigrate between the resins.

In some embodiments, a resin layer or interlayer can include at least afirst resin layer comprising a first poly(vinyl acetal) resin and afirst plasticizer, and a second resin layer, adjacent to the first resinlayer, comprising a second poly(vinyl acetal) resin and a secondplasticizer. The first and second plasticizer can be the same type ofplasticizer, or the first and second plasticizers may be different. Insome embodiments, at least one of the first and second plasticizers mayalso be a blend of two or more plasticizers, which can be the same as ordifferent than one or more other plasticizers. When one of the first andsecond poly(vinyl acetal) resins has a residual hydroxyl content that isat least 2 weight percent higher or lower than the residual hydroxylcontent of the other, the difference in plasticizer content between theresin layers can be at least about 2, at least about 5, at least about8, at least about 10, at least about 12, or at least about 15 phr. Inmost embodiments, the resin layer that includes the resin having a lowerhydroxyl content can have the higher plasticizer content. In order tocontrol or retain other properties of the resin layer or interlayer, thedifference in plasticizer content between the first and second resinlayers may be not more than about 40, not more than about 30, not morethan about 25, not more than about 20, or not more than about 17 phr. Inother embodiments, the difference in plasticizer content between thefirst and second resin layers can be at least about 40, at least about50, at least about 60, or at least about 70 phr.

As a result, in some embodiments, wherein the first and secondpoly(vinyl acetal) resins are present in adjacent layers of a multilayerinterlayer, the first and second resin layers can exhibit differentglass transition temperatures. Similarly, when the first and secondpoly(vinyl acetal) resins are present in a blend, the domains of one ofthe first and second poly(vinyl acetal) resins can exhibit a differentglass transition temperature than the other of the first and secondpoly(vinyl acetal) resins. Glass transition temperature, or T_(g), isthe temperature that marks the transition from the glass state of thepolymer to the rubbery state. The glass transition temperatures of theresins and layers described herein were determined by dynamic mechanicalthermal analysis (DTMA). The DTMA measures the storage (elastic) modulus(G′) in Pascals, loss (viscous) modulus (G″) in Pascals, and the tandelta (G″/G′) of the specimen as a function of temperature at a givenoscillation frequency and temperature sweep rate. The glass transitiontemperature is then determined by the position of the tan delta peak onthe temperature scale. Glass transition temperatures provided hereinwere determined at an oscillation frequency of 1 Hz under shear mode anda temperature sweep rate of 3° C./min.

The difference in the glass transition temperature of the first resinlayer and the second resin layer, or between various regions of ablended resin or resin layer, can be at least about 3, at least about 5,at least about 8, at least about 10, at least about 12, at least about15, at least about 18, at least about 20, at least about 22, or at leastabout 25° C. One of the first and second resin layers can have a glasstransition temperature of at least about 26, at least about 28, at leastabout 30, at least about 33, at least about 35° C. and/or not more thanabout 70, not more than about 65, not more than about 60, not more thanabout 55, not more than about 50° C., or in the range of from about 26to about 70, about 30 to about 60, about 35 to about 50° C. The other ofthe first and second poly(vinyl acetal) resins can have a glasstransition temperature of not more than 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 0, not more than about −5, or not more than about −10°C.

When the first and second poly(vinyl acetal) resins are blended with oneanother such that domains of one resin are dispersed within the other,such differences in plasticizer content and/or glass transitiontemperature may also exist between domains of the first and secondresins. For example, in some embodiments, a resin layer or interlayermay include various domains of higher or lower plasticizer contentand/or domains having higher or lower glass transition temperatures, asdescribed previously. In some embodiments, at least a portion of theresin layer or interlayer can have a glass transition temperature of atleast about 26, at least about 28, at least about 30, at least about 33,at least about 35° C. and/or not more than about 70, not more than about65, not more than about 60, not more than about 55, not more than about50° C., or in the range of from about 26 to about 70, about 28 to about60, about 35 to about 50° C. and/or at least a portion of the resinlayer or interlayer can have a glass transition temperature of not morethan 25, not more than about 20, not more than about 15, not more thanabout 10, not more than about 5, not more than about 0° C., not morethan about −5° C., or not more than about −10° C.

One or more resin blends, layers, and interlayers described herein mayinclude various other additives to impart particular properties orfeatures to the interlayer. Such additives can include, but are notlimited to, dyes, pigments, stabilizers such as ultraviolet stabilizers,antioxidants, anti-blocking agents, flame retardants, IR absorbers orblockers such as indium tin oxide, antimony tin oxide, lanthanumhexaboride (LaB₆) and cesium tungsten oxide, processing aides, flowenhancing additives, lubricants, impact modifiers, nucleating agents,thermal stabilizers, UV absorbers, dispersants, surfactants, chelatingagents, coupling agents, adhesives, primers, reinforcement additives,and fillers.

Additionally, various adhesion control agents (“ACAs”) can be used inthe interlayers of the present disclosure to control the adhesion of thesheet to glass. In various embodiments, the amount of ACAs present in aresin composition, layer, or interlayer can be at least about 0.003, atleast about 0.01, at least about 0.025 and/or not more than about 0.15,not more than about 0.10, or not more than about 0.04 phr, or in therange of from about 0.003 to about 0.15, about 0.01 to about 0.10, orabout 0.025 to about 0.04 phr. Suitable ACAs can include, but are notlimited to, sodium acetate, potassium acetate, magnesium bis(2-ethylbutyrate), magnesium bis(2-ethylhexanoate), and combinations thereof, aswell as the ACAs disclosed in U.S. Pat. No. 5,728,472.

Resins having different compositions and plasticized resin layers havingdifferent properties also tend to exhibit different refractive indices,which can reduce the optical quality of the resulting layer or blend.Although not wishing to be bound by theory, it is believed that suchdifferences in refractive index may cause light that passes through thedifferent resin layers or domains to be refracted in differentdirections, which may cause haze in the final product. At times, theabsolute value of the difference between the refractive index of thefirst poly(vinyl acetal) resin or layer and the refractive index of thesecond poly(vinyl acetal) resin or layer, measured according to ASTMD542 at a wavelength of 589 nm and 25° C., can exceed 0.010. As aresult, these compositions, layers, or interlayers can have a haze valuegreater than 5 percent and/or a mottle value greater than 3.

However, in various embodiments of the present invention, compositions,layers, and interlayers comprising a poly(vinyl acetal) resin mayfurther include at least one refractive index (RI) balancing agent foradjusting the refractive index of the composition, layer, or interlayer.In some embodiments, the composition, layer, or interlayer may includeat least a first poly(vinyl acetal) resin and a second poly(vinylacetal) resin along with at least one RI balancing agent. In otherembodiments, the composition, layer, or interlayer ma include a singlepoly(vinyl acetal) resin along with at least one RI balancing agent. Asdiscussed above, the RI balancing agent can be any suitable agentpresent in a resin or a resin blend, layer, or interlayer, or portionthereof, that increases or reduces the refractive index of at least oneresin or layer, which may improve the optical properties of theinterlayer as compared to an identical interlayer formed without an RIbalancing agent. In some embodiments, the resin blend, layer, orinterlayer may have a haze value of at least 5 percent when formed inthe absence of the RI balancing agent.

The RI balancing agent can be in any suitable form and may be physicallyblended with one or more resins or it can be chemically bonded, orreacted, with at least one resin so that the RI balancing agent isincorporated into the polymer chain. Examples of RI balancing agents caninclude, but are not limited to, liquid RI additives, solid RIadditives, and residues of at least one aldehyde present in one or moreof the poly(vinyl acetal) resins. Various embodiments of RI balancingagents, as well as resin compositions, layers, and interlayers includingthe same, will now be discussed in detail below.

The RI balancing agent may be present in the resin, resin layer, orinterlayer in an amount sufficient to modify the refractive index ofpoly(vinyl acetal) resin, resin layer, or interlayer. The RI balancingagent may also be present in the composition, layer, or interlayer in anamount sufficient to modify the refractive index of at least one of thetwo poly(vinyl acetal) resins, thereby minimizing the difference betweenthe refractive indices of two poly(vinyl acetal) resin layers havingdifferent refractive indices. The RI balancing agent may also minimizethe difference between the refractive index of one or more poly(vinylacetal) resins and one or more plasticizers within a resin composition,layer, or interlayer. In some embodiments, the RI balancing agent may bepresent in an amount sufficient to reduce the absolute value of thedifference between the refractive index the first poly(vinyl acetal)resin layer and the refractive index of the second poly(vinyl acetal)resin layer to not more than 0.010, not more than about 0.009, not morethan about 0.008, not more than about 0.007, not more than about 0.006,not more than about 0.005, not more than about 0.004, or not more thanabout 0.003. When a multilayer interlayer includes two or more resinlayers, the RI balancing agent may be present in one or both layers andcan, in some embodiments, be present in one of the layers in a higheramount than in one or more of the other layers.

In some embodiments, the RI balancing agent can comprise one or moreresidues of an aldehyde having a refractive index of at least 1.421, asmeasured by ASTM D542 at a wavelength of 589 nm and a temperature of 25°C. The RI balancing aldehyde, which may also be referred to herein as a“high refractive index aldehyde” or “high RI aldehyde,” can have arefractive index of at least about 1.425, at least about 1.450, at leastabout 1.475, at least about 1.500, at least about 1.510, or at leastabout 1.515 and/or not more than about 1.675, not more than about 1.650,or not more than about 1.625, or in the range of from about 1.425 toabout 1.675, about 1.475 to about 1.650, or about 1.515 to about 1.625.The high RI aldehyde may be an aromatic aldehyde that includes at leastone aromatic ring or group. Examples of aromatic aldehydes can include,but are not limited to, C₇ to C₃₀ aromatic aldehydes, C₈ to C₂₅ aromaticaldehydes, or C₉ to C₂₀ aromatic aldehydes. Specific examples of high RIaldehydes that can be used as RI balancing agents in various embodimentsof the present invention are listed in Table 1, below.

TABLE 1 Exemplary High RI Aldehydes Aldehyde Refractive IndexHexylcinnamaldehyde 1.517 Benzaldeyde 1.545 Cinnamaldehyde 1.6204-Chlorobenzaldehyde 1.585 4-t-butylphenylacetaldehyde 1.5302-phenylpropionaldehyde 1.517 Hydrocinnamaldehyde 1.523

When the RI balancing agent includes residues of at least one high RIaldehyde, at least one of the first and second poly(vinyl acetal) resinscan include residues of at least one high RI aldehyde in an amount of atleast about 0.5, at least about 1, at least about 5, at least about 10,at least about 15, at least about 20, at least about 25, at least about30, at least about 35, at least about 40, at least about 45, at leastabout 50, at least about 55, at least about 60, at least about 65, atleast about 70, at least about 75, at least about 80, at least about 85,at least about 90, at least about 95 percent and/or not more than about99.5, not more than about 99, not more than about 97, not more thanabout 95, not more than about 90, not more than about 85, not more thanabout 80, not more than about 75, not more than about 70, not more thanabout 65, or not more than about 60 weight percent, based on the totalweight of aldehyde residues of the first or second poly(vinyl acetal)resin. At least one of the first and second poly(vinyl acetal) resinscan include residues of at least one high RI aldehyde in an amount inthe range of from about 0.5 to about 99.5, about 10 to about 90, about25 to about 75, or about 40 to about 60 weight percent, based on thetotal weight of aldehyde residues of the first or second poly(vinylacetal) resin.

The amount of high RI aldehyde residues can be determined using acombination of Fourier Transform Infrared Spectroscopy (FT-IR) and SizeExclusion Chromatography (SEC) with UV detection. In particular, FT-IRis used to measure residual hydroxyl and residual acetate contents ofthe resin and SEC is used to determine the amount of high RI aldehyderesidues, with the amount of any other aldehyde residues beingdetermined by the difference. The FT-IR analysis is performed using aPerkin Elmer Spectrum 100 FT-IR Spectrometer (commercially availablefrom Perkin Elmer, Waltham, Mass.) with an ATR sampling attachment. Theanalysis is performed using 8 scans at a 4 cm-1 resolution. Prior totesting, a calibration is generated from several poly(vinyl n-butyral)samples of varying residual hydroxyl and residual acetate contents whichhave been dried in a desiccator with silica overnight at roomtemperature to remove excess moisture. The peak maximum wave number ofthe hydroxyl stretching band and the carbonyl stretching band arerespectively correlated with the molar vinyl alcohol content and vinylacetate content of each sample, which was previously determined by ASTMD1396, and the resulting linear curve fits are used to predict molarresidual hydroxyl content and molar residual acetate content of thesamples being analyzed. These values can be converted to weight percentby calculation after determination of the composition of the poly(vinylacetal) resin using SEC analysis has been completed, as described below.

The SEC analysis is performed using a Waters 2695 Alliance pump andautosampler with a Waters 410 inline differential refractive indexdetector and a Waters 2998 PDA inline UV detector (commerciallyavailable from Waters Corporation, Milford, Mass.) with DionexChromeleon v. 6.8 data acquisition software with an extension pack(commercially available from Thermo Fischer Scientific, Sunnyvale,Calif.). The analysis is performed with a PL Gel Mixed C (5 micron)column and Mixed E (3 micron) columns with an injection volume of 50microliters at a flow rate of 1.0 mL/minute. Samples are prepared bydissolving between 0.03 and 0.09 grams of resin in 10-15 mL ofstabilized tetrahydrofuran and then filtering each through a 0.22 micronPTFE filter. Initial calibrations of the chromatograph are performedusing a narrow molecular weight polystyrene standard and a poly(vinylacetal) resin including only residues of the high RI aldehyde, andsubsequent samples were calibrated with a broad molecular weightpolystyrene (commercially available as PSBR250K from American PolymerStandard Corporation, Mentor, Ohio).

In some embodiments, only one of the first and second poly(vinyl acetal)resins includes residues of the high RI aldehyde, while, in otherembodiments, both of the resins may include such residues. Therefractive index of a resin comprising residues of a high RI aldehydecan be at least about 1.492, at least about 1.495, at least about 1.500,at least about 1.505, at least about 1.510, or at least about 1.515.

In various embodiments, at least one of the first and second poly(vinylacetal) resins may also include residues of at least one aldehyde havinga refractive index of less than 1.421. Examples of these aldehydes caninclude, for example, aliphatic aldehydes such as the C₄ to C₈ aldehydesdiscussed above. The aldehydes having a refractive index of less than1.421 can be selected from the group consisting of n-butyraldehyde,iso-butyraldehyde, and 2-ethylhexyl aldehyde.

When these residues are present, the first and/or second poly(vinylacetal) resin can include at least about 10, at least about 15, at leastabout 20, at least about 25, at least about 30, at least about 35, atleast about 40, at least about 45, at least about 50, at least about 55,at least about 60, at least about 65, at least about 70, at least about75, at least about 80, at least about 85, at least about 90, at leastabout 95 percent and/or not more than about 99, not more than about 97,not more than about 95, not more than about 90, not more than about 85,not more than about 80, not more than about 75, not more than about 70,not more than about 65, or not more than about 60 weight percent, ofthese aldehydes, based on the total weight of aldehyde residues of thefirst or second poly(vinyl acetal) resin.

The amount of residues of an aldehyde having a refractive index of lessthan 1.421 are determined using the FT-IR/SEC method described above andthen by calculation according to the following formula: 100 weightpercent−weight percent residual hydroxyl (from FT-IR)−weight percent ofhigh RI aldehyde residues (from SEC)−weight percent residual acetate(from FT-IR)=weight percent of residues of aldehyde having refractiveindex less than 1.421. The first and/or second poly(vinyl acetal) resincan include residues of an aldehyde having a refractive index of lessthan 1.421 in an amount in the range of from about 10 to about 99, about25 to about 75, or about 40 to about 60 weight percent, based on thetotal weight of aldehyde residues of the first or second poly(vinylacetal) resin. The refractive index of one of these resins can be lessthan about 1.492, less than about 1.491, or less than about 1.490,measured as described previously.

According to some embodiments, one of the first and second poly(vinylacetal) resins primarily includes residues of a high RI aldehyde, whilethe other of the first and second poly(vinyl acetal) resins primarilyincludes residues of at least one aldehyde having a refractive index ofless than 1.421. As used herein, the term “primarily” means at least 75weight percent, so that a poly(vinyl acetal) resin primarily includingresidues of a specified aldehyde includes at least 75 weight percent ofresidues of the specified aldehyde, based on the total weight ofaldehyde residues of that resin. The poly(vinyl acetal) resin primarilyincluding residues of a high RI aldehyde can include not more than about25, not more than about 20, not more than about 15, not more than about10, not more than about 5, not more than about 2, or not more than about1 weight percent of residues of other aldehydes having a refractiveindex less than 1.421, based on the total weight of aldehyde residues ofthe resin.

Similarly, the other poly(vinyl acetal) resin, which can primarilyinclude residues of an aldehyde having a refractive index of less than1.421, may comprise not more than about 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 2, or not more than about 1 weight percent of residuesof a high RI aldehyde, based on the total weight of aldehyde residues ofthe resin, and may include at least about 75, at least about 80, atleast about 85, at least about 90, at least about 95, at least about 97,or at least about 99 percent of residues of one or more aldehydes havinga refractive index less than 1.421. In some embodiments, the ratio ofthe resin primarily including residues of the high RI aldehyde to theother resin or resins in the composition can be at least about 1:99, atleast about 5:95, at least about 10:90, at least about 20:80, at leastabout 25:75, at least about 30:70, at least about 40:60 and/or not morethan about 99:1, not more than about 95:5, not more than about 90:10,not more than about 85:15, not more than about 75:25, not more thanabout 70:30, or not more than about 60:40, or in the range of from about1:99 to 99:1, about 10:90 to about 90:10, about 25:75 to 75:25, or about40:60 to 60:40.

In other embodiments, at least one of the first and second poly(vinylacetal) resins includes residues of a high RI aldehyde and at least onealdehyde having a refractive index of less than 1.421, thereby forming a“hybrid” resin that includes residues of both high and low RI aldehydes.According to these embodiments, the amounts of the high RI aldehyderesidues and the residues of aldehydes having a refractive index of lessthan 1.421, as well as the weight ratios of one to the other, in thehybrid resin can be within the same ranges provided above with respectto the resin blends. When the first or second poly(vinyl acetal) resinincludes residues of both high RI and lower RI aldehydes, the other ofthe two poly(vinyl acetal) resins may also include residues of at leastone high RI aldehyde. Alternatively, the other of the two resins mayinclude little or no high RI aldehyde residues, such that it includesless than about 10, less than about 5, less than about 2, or less thanabout 1 weight percent of residues of a high RI aldehyde, with thebalance being residues of an aldehyde having a refractive index of lessthan 1.421, including, for example, aldehydes selected from the groupconsisting of n-butyraldehyde, iso-butyraldehyde, 2-ethylhexyl aldehyde,and combinations thereof.

When the interlayer is a multilayer interlayer, it can include at leastone resin layer having at least a first poly(vinyl acetal) resin andanother resin layer comprising at least a second poly(vinyl acetal)resin, wherein the difference between the residual hydroxyl content ofthe first poly(vinyl acetal) resin and the second poly(vinyl acetal)resin is at least 2 weight percent. One or both of the poly(vinylacetal) resins can include residues of a high RI aldehyde and one of theresin layers may have a refractive index that is higher or lower thanthe other by at least about 0.002, at least about 0.003, at least about0.004 and/or not more than about 0.010, not more than about 0.009, notmore than about 0.008, or not more than about 0.007, or by an amount inthe range of from about 0.002 to about 0.010, about 0.003 to about0.009, or about 0.004 to about 0.007. In some embodiments when theinterlayer includes at least three resin layers, the innermost resinlayer can have the higher refractive index, while in other embodiments,the refractive index of one or both of the outer resin layers may behigher. In some embodiments, only one of the first and second poly(vinylacetal) resins may include residues of the high RI aldehyde. In otherembodiments, both of the poly(vinyl acetal) resins may include residuesof at least one high RI aldehyde, but the resins can still exhibit adifference in refractive index within the ranges provided above.

One or both of the poly(vinyl acetal) resins can include residues of atleast one high RI aldehyde. In some embodiments, when the poly(vinylacetal) resin including such residues has a residual hydroxyl content ofnot more than, for example, 15 weight percent, the resin layer includingsuch a resin may have a glass transition temperature of less than 20,not more than about 15, not more than about 10, not more than about 5,not more than about 0, not more than about −5, or not more than about−10° C. and a refractive index of at least about 1.465, at least about1.470, at least about 1.475, at least about 1.480, at least about 1.485,or at least about 1.490, each measured as described previously. Theplasticizer content of the layer, according to various embodiments, canbe at least about 50, at least about 55, at least about 60, at leastabout 65 phr and/or not more than about 120, not more than about 110,not more than about 90, not more than about 85, not more than about 80,or not more than about 75 phr, or in the range of from about 50 to about120, about 55 to about 110, about 60 to about 90, or about 65 to about75 phr.

When the resin having the residues of a high RI aldehyde in themultilayer interlayer discussed above has a residual hydroxyl contentgreater than, for example 16 weight percent, the resin layer includingthat resin may have a glass transition temperature of at least about 26,at least about 30, at least about 33, or at least about 35° C., and arefractive index of at least about 1.470, at least about 1.475, at leastabout 1.480, at least about 1.485, or at least about 1.490, eachmeasured as described previously. The plasticizer content of the layer,according to some embodiments, can be less than 50 phr, not more thanabout 45 phr, not more than about 40 phr, not more than about 30, notmore than about 20 phr.

According to various embodiments of the present invention, the RIbalancing agent can comprise a liquid RI balancing agent. As usedherein, the term “liquid RI balancing agent” refers to an RI balancingagent that is liquid at standard conditions of 25° C. and 1 atm. In someembodiments, the liquid RI balancing agent can be, for example, a highRI plasticizer. As used herein, the term “high RI plasticizer,” refersto a plasticizer having a refractive index of at least 1.460, measuredas described previously. The high RI plasticizers suitable for use as RIbalancing agents can have a refractive index of at least about 1.470, atleast about 1.480, at least about 1.490, at least about 1.500, at leastabout 1.510, at least about 1.520 and/or not more than about 1.600, notmore than about 1.575, or not more than about 1.550, measured asdiscussed above. The refractive index of the high RI plasticizers may bein the range of from about 1.460 to about 1.600, about 1.470 to about1.575, about 1.480 to about 1.550, about 1.490 to about 1.525.

Examples of types or classes of high RI plasticizers can include, butare not limited to, polyadipates (RI of about 1.460 to about 1.485);epoxides such as epoxidized soybean oils (RI of about 1.460 to about1.480); phthalates and terephthalates (RI of about 1.480 to about1.540); benzoates and toluates (RI of about 1.480 to about 1.550); andother specialty plasticizers (RI of about 1.490 to about 1.520).Specific examples of suitable RI plasticizers can include, but are notlimited to, dipropylene glycol dibenzoate, tripropylene glycoldibenzoate, polypropylene glycol dibenzoate, isodecyl benzoate,2-ethylhexyl benzoate, diethylene glycol benzoate, butoxyethyl benzoate,butoxyethyoxyethyl benzoate, butoxyethoxyethoxyethyl benzoate, propyleneglycol dibenzoate, 2,2,4-trimethyl-1,3-pentanediol dibenzoate,2,2,4-trimethyl-1,3-pentanediol benzoate isobutyrate, 1,3-butanedioldibenzoate, diethylene glycol di-o-toluate, triethylene glycoldi-o-toluate, dipropylene glycol di-o-toluate, 1,2-octyl dibenzoate,tri-2-ethylhexyl trimellitate, di-2-ethylhexyl terephthalate, bis-phenolA bis(2-ethylhexaonate), di-(butoxyethyl) terephthalate,di-(butoxyethyoxyethyl) terephthalate, and mixtures thereof. The high RIplasticizer may be selected from dipropylene glycol dibenzoate andtripropylene glycol dibenzoate, and/or 2,2,4-trimethyl-1,3-pentanedioldibenzoate.

When the resin layer or interlayer includes a high RI plasticizer, theplasticizer can be present in the layer alone or it can be blended withone or more additional plasticizers. The other plasticizer orplasticizers may also comprise high RI plasticizers, or one or more maybe a lower RI plasticizer having a refractive index of less than 1.460.In some embodiments, the lower RI plasticizer may have a refractiveindex of less than about 1.450, less than about 1.445, or less thanabout 1.442 and can be selected from the group listed previously. When amixture of two or more plasticizers are employed as a RI balancingagent, the mixture can have a refractive index within one or more of theabove ranges.

When used as an RI balancing agent in a multilayer interlayer, a high RIplasticizer may be present in different amounts in two or more of theresin layers. Similarly, when used as an RI balancing agent in a resincomposition or blended resin layer, the high RI plasticizer may bepartitioned as described previously, such that resin layers or domainshaving a lower residual hydroxyl content may have higher amounts of thehigh RI plasticizer. In some embodiments, at least one layer or portionof a resin layer or interlayer may comprise a high RI plasticizer as anRI balancing agent in an amount of at least about 5, at least about 10,at least about 15, at least about 20, at least about 25, at least about30, at least about 35 and/or not more than about 50, not more than about45, or not more than about 40 phr. The high RI plasticizer can bepresent in the resin layer or interlayer in an amount in the range offrom about 5 to about 50, about 10 to about 45, about 20 to about 40phr. In some embodiments, one or more other layers or portions caninclude the high RI plasticizer in an amount of at least about 50, atleast about 55, at least about 60, at least about 65, at least about 70and/or not more than about 120, not more than about 110, not more thanabout 100, not more than about 90, or not more than about 75 phr, or inthe range of from about 50 to about 120, about 55 to about 110, about 60to about 90, about 65 to about 75 phr. These amounts may include anyother plasticizers present in the composition, including those having arefractive index less than 1.460, or may include only the high RIplasticizer.

When a high RI plasticizer is used as an RI balancing agent in amultilayer interlayer, the interlayer can include at least one resinlayer having a first poly(vinyl acetal) resin and another resin layercomprising a second poly(vinyl acetal) resin, wherein the differencebetween the residual hydroxyl content of the first poly(vinyl acetal)resin and the second poly(vinyl acetal) resin is at least 2 weightpercent. At least one of the resin layers can include a high RIplasticizer in an amount sufficient so that the absolute value of thedifference between the refractive index of the resin layer and therefractive index of the another resin layer is not more than 0.010. Insome embodiments when the interlayer includes at least three resinlayers, the innermost resin layer can have a higher refractive index,while in other embodiments, the refractive index of one or both of theouter resin layers may be higher.

When a high RI plasticizer is included in a resin layer that includes atleast one poly(vinyl acetal) resin having the lower residual hydroxylcontent, at least a portion of the resin layer can have a glasstransition temperature of not more than 25, not more than about 20, notmore than about 15, not more than about 10, not more than about 5, notmore than about 0, not more than about −5, or not more than about −10°C., and the layer can have a refractive index of at least about 1.465,at least about 1.470, at least about 1.475, at least about 1.480, atleast about 1.485, or at least about 1.490, measured as describedpreviously. The plasticizer content of this layer, in some embodiments,can be at least about 50, at least about 55, at least about 60 phrand/or not more than about 120, not more than about 110, not more thanabout 90, not more than about 85, not more than about 80, or not morethan about 75 phr, or in the range of from about 50 to about 120, about55 to about 110, about 60 to about 90, or about 60 to about 75 phr.

When the high RI plasticizer is present in the resin layer thatcomprises the poly(vinyl acetal) resin having a higher residual hydroxylcontent, at least a portion of the layer can have a glass transitiontemperature of at least about 26, at least about 30, at least about 33,or at least about 35° C., and the layer can have a refractive index ofat least about 1.470, at least about 1.475, at least about 1.480, atleast about 1.485, or at least about 1.490, measured as describedpreviously. The plasticizer content of this layer, according to someembodiments, can be less than 50 phr, not more than about 45 phr, notmore than about 40 phr, not more than about 30, or not more than about20 phr.

According to various embodiments of the present invention, the RIbalancing agent may be a solid RI additive present in one or more layersor portions of a layer or interlayer. As used herein, the term “solid RIadditive” refers to an additive used to adjust the refractive index of apoly(vinyl acetal) resin, resin layer, or interlayer and which is solidat ambient conditions of 25° C. and 1 atm. In various embodiments, thesolid RI additive may have a melting point of at least about 27, atleast about 30, at least about 35, at least about 40, at least about 45,at least about 50, at least about 55, at least about 60, at least about75, at least about 80, at least about 85, at least about 90, at leastabout 95, or at least about 100° C. When employed in a resin blend,layer, or interlayer, the solid RI additive can be present in an amountsufficient such that the absolute value of the difference between therefractive indices of the first and second resin layers is not more thanabout 0.010. The difference between the refractive index of the firstand second resin layers may be greater than 0.010, when formulated intoidentical resin layers in the absence of the solid RI additive.

In some embodiments, the solid RI additive can be a high RI solidadditive for increasing the refractive index of at least one resin layeror interlayer. The refractive index of the high RI solid additive can beat least about 1.460, at least about 1.465, at least about 1.470, atleast about 1.475, at least about 1.480, at least about 1.485, at leastabout 1.490, at least about 1.495, at least about 1.500, at least about1.505, at least about 1.510, at least about 1.525, at least about 1.550,at least about 1.575, or at least about 1.600, measured as describedpreviously. In other embodiments, the solid RI additive may be a RIlowering solid additive for reducing the refractive index of at leastone resin or resin layer. The RI lowering solid additive can have arefractive index of less than 1.460, not more than about 1.455, not morethan about 1.450, not more than about 1.445, or not more than about1.440, measured as described previously. Whether higher or lower, thesolid RI additive can have a refractive index that is at least about0.005, at least about 0.010, at least about 0.050, at least about 0.10and/or not more than about 0.50, not more than about 0.35, or not morethan about 0.20 different than the refractive index of the poly(vinylacetal) resin. The difference in refractive index between the solid RIadditive and the poly(vinyl acetal) resin can be in the range of fromabout 0.005 to about 0.50, about 0.010 to about 0.35, or about 0.050 toabout 0.35.

In various embodiments, the solid RI additive can be present in a resincomposition or interlayer in an amount of at least about 0.5, at leastabout 1, at least about 1.5, at least about 2, or at least about 5 phr,depending on the specific type of additive and layer or interlayer. Thesolid RI additive, whether a high RI additive or an RI loweringadditive, may comprise a physical solid RI additive capable of beingphysically mixed or blended with at least one poly(vinyl acetal) resinin a resin composition or layer, or it can be a reactive solid RIadditive, which may react with and become incorporated into the backboneof one or more poly(vinyl acetal) resins.

The solid RI additive can be used in combination with one or more low RIplasticizers. Examples of low RI plasticizers can include, but are notlimited to, triethylene glycol di-(2-ethylhexanoate) (“3GEH”),triethylene glycol di-(2-ethylbutyrate), triethylene glycoldiheptanoate, tetraethylene glycol diheptanoate, tetraethylene glycoldi-(2-ethylhexanoate) (“4GEH”), dihexyl adipate, dioctyl adipate, hexylcyclohexyladipate, diisononyl adipate, heptylnonyl adipate,di(butoxyethyl) adipate, and bis(2-(2-butoxyethoxy)ethyl) adipate,dibutyl sebacate, dioctyl sebacate, and mixtures thereof. Theplasticizer may be selected from the group consisting of triethyleneglycol di-(2-ethylhexanoate) and tetraethylene glycoldi-(2-ethylhexanoate), or the plasticizer can comprise triethyleneglycol di-(2-ethylhexanoate). The solid RI additive can also be used incombination with one or more high RI plasticizers mentioned previously.

When the solid RI additive is a physical solid RI additive, it may becombined with one or more poly(vinyl acetal) resins or layers in aninterlayer. In some embodiments, the physical solid RI additive may bepresent in at least one layer or in an interlayer in an amount of atleast about 1, at least about 2, at least about 3, at least about 5, atleast about 8, at least about 10, at least about 12, at least about 15,at least about 20 and/or not more than about 60, not more than about 55,not more than about 50, not more than about 45, not more than about 40,not more than about 35, not more than about 30, not more than about 25,not more than about 20, or not more than about 15 phr, or in an amountin the range of from about 1 to about 60, about 5 to about 50, or about10 to about 45 phr. Examples of suitable physical solid high RIadditives can include, but are not limited to, polyadipates, polystyrenehaving a molecular weight of less than 2500, epoxides, phthalic acidesters, benzoic acid esters, inorganic oxides such as, for example,zirconium oxide, and combinations thereof. Physical solid RI loweringadditives can be selected from the group consisting of halogenatedadditives, and silicon-containing additives.

When utilized in a multilayer interlayer, the physical solid RI additivemay be present in one of the resin layers in a higher amount than one ormore other layers. The difference between the amount of the physicalsolid RI additive present in one of the resin layers and the amount ofphysical solid RI additive present in another layer, including, forexample, an adjacent layer, can be at least about 2, at least about 5,at least about 8, at least about 10 phr and/or not more than about 30,not more than about 25, or not more than about 20 phr, or it can be inthe range of from about 2 to about 30, about 5 to about 25, or about 10to about 20 phr. According to some embodiments, at least one of thelayers can include at least about 1, at least about 5, at least about10, at least about 15 phr and/or not more than about 60, not more thanabout 55, not more than about 50, not more than about 45 phr of thephysical solid RI additive, or the physical solid RI additive can bepresent in an amount in the range of from about 1 to about 60, about 10to about 50, or about 15 to about 45 phr. In some embodiments, thephysical solid RI additive can be present in one or more layers in anamount of at least about 5, at least about 10, at least about 15, atleast about 20 phr and/or not more than about 60, not more than about55, not more than about 50 phr, or in an amount in the range of fromabout 5 to about 60, about 15 to about 55, or about 20 to about 50 phr.

When the multilayer interlayer comprises three or more resin layers andthe solid RI additive is a solid high RI additive, the inner, or core,layer or layers can include higher amounts of the physical solid RIadditive than the outer, or skin, layers. However, if the solid RIadditive is a solid RI lowering additive, the outer skin layers mayinclude higher amounts of the solid RI additive than the inner corelayer. The core layer can include at least about 30, at least about 40,at least about 50, at least about 60, at least about 70, or at leastabout 80 percent of the total amount of physical solid RI additivepresent in the interlayer.

When the solid RI additive is a reactive solid RI additive, it may bereacted with at least one poly(vinyl acetal) resin such that at least aportion of the additive is incorporated into the polymer chain. Thereactive RI additive can be an aromatic additive and can comprise, insome embodiments, phthalic anhydrides and phenylalkoxysilanes including,for example, diphenyldimethoxysilane.

In some embodiments, the reactive RI additive may be present in onelayer of a multilayer interlayer in a higher amount than it is presentin one or more other layers of the interlayer. In some embodiments, itmay be absent, or substantially absent, from one or more resin layers.For example, when the interlayer is a multilayer interlayer including atleast three resin layers, the inner core layer may include at leastabout 0.5, at least about 1, at least about 1.5, at least about 2, atleast about 2.5, at least about 3 and/or not more than about 50, notmore than about 30, not more than about 20, not more than about 15, notmore than about 12, not more than about 10, or not more than about 8 phrof one or more reactive solid RI additives, or an amount in the range offrom about 0.5 to about 20, about 1 to about 12, or about 2 to about 8phr. The outer skin layer or layers may include not more than about 10,not more than about 5, not more than about 2, not more than about 1, ornot more than about 0.5 phr of the reactive solid RI additive. The corelayer can include at least about 65, at least about 75, at least about85, at least about 95, or at least about 99 percent of the total amountof the reactive RI additive present in the interlayer.

When a solid RI additive is used as an RI balancing agent in amultilayer interlayer, the interlayer can include at least one resinlayer having a first poly(vinyl acetal) resin and another resin layercomprising a second poly(vinyl acetal) resin, wherein the differencebetween the residual hydroxyl content of the first poly(vinyl acetal)resin and the second poly(vinyl acetal) resin is at least 2 weightpercent. At least one of the resin layers can include the high RIadditive in an amount sufficient so that the absolute value of thedifference between the refractive index of the first resin layer and therefractive index of the second resin layer is not more than 0.010. Insome embodiments when the interlayer includes at least three resinlayers, the innermost resin layer can have a higher refractive index,while in other embodiments, the refractive index of one or both of theouter resin layers may be higher.

When a solid RI additive is included in a resin layer comprising thepoly(vinyl acetal) resin having the lower residual hydroxyl content, theresin layer can have a glass transition temperature of not more than 25,not more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 0, not more than about −5, ornot more than about −10° C., and a refractive index of at least about1.465, at least about 1.470, at least about 1.475, at least about 1.480,at least about 1.485, at least about 1.495, or at least about 1.500,each measured as described previously. The plasticizer content of thislayer, in some embodiments, can be at least about 50, at least about 55,at least about 60, at least about 65 phr and/or not more than about 120,not more than about 110, not more than about 90, not more than about 85,not more than about 80, or not more than about 75 phr, or in the rangeof from about 50 to about 120, about 55 to about 110, about 60 to about90, about 65 to about 75 phr.

When the solid RI additive is present in the resin layer that comprisesthe poly(vinyl acetal) resin having a higher residual hydroxyl content,the layer can have a glass transition temperature of at least about 26,at least about 30, at least about 33, or at least about 35° C. In someembodiments, the layer can have a refractive index of at least about1.470, at least about 1.475, at least about 1.480, at least about 1.485,at least about 1.490, at least about 1.500, at least about 1.510. Theplasticizer content of this layer, according to some embodiments, can beless than 50 phr, not more than about 45 phr, not more than about 40phr, not more than about 30, or not more than about 20 phr.

Resin compositions, layers, and interlayers formulated according tovarious embodiments of the present invention to include at least twopoly(vinyl acetal) resins and an RI balancing agent can exhibit enhancedoptical properties without sacrificing other properties such as impactresistance and acoustic performance. As discussed above, due todifferences in properties or composition of the resins, such as, forexample, residual hydroxyl content, residual acetate content, oraldehyde residues, identical blends of the same resins formulatedwithout the RI balancing agent may provide compositions, layers, andinterlayers with reduced optical performance.

Clarity is one parameter used to describe the optical performance ofcompositions, layers, and interlayers described herein and may bedetermined by measuring haze value or percent. Haze value represents thequantification of light scattered by a sample in contrast to theincident light. In some embodiments, the resin blends, layers, andinterlayers described herein may have a haze value of less than 5percent, less than about 4 percent, less than about 3 percent, less thanabout 2 percent, less than about 1, or less than about 0.5 percent, asmeasured in accordance with ASTM D1003-13—Procedure B using IlluminantC, at an observer angle of 2 degrees. The test is performed with aspectrophotometer, such as a Hunterlab UltraScan XE instrument(commercially available from Hunter Associates, Reston, Va.), on apolymer sample having a thickness of 0.76 mm, which has been laminatedbetween two sheets of clear glass each having a thickness of 2.3 mm(commercially available from Pittsburgh Glass Works of Pennsylvania).

Additionally, the resin layers and interlayers described herein may havea mottle value of not more than 3, not more than 2, or not more than 1.Mottle is another measure of optical quality, which is detected as atexture or graininess. Mottle is a visual defect if the level is toohigh or too severe, thereby causing objectionable visual appearance.Mottle is assessed and categorized by a side-by-side qualitativecomparison of shadowgraph projections for a test laminate with a set ofstandard laminate shadowgraphs that represent a series, or scale, ofmottle values ranging from 1 to 4, with 1 representing a standard of lowmottle (i.e., a low number of disruptions) and 4 representing a standardof high mottle (i.e., a high number of disruptions). High mottle isgenerally considered objectionable, particularly in automotive andarchitectural applications. Optionally, a model laminate having a singlelayer interlayer with zero mottle (no mottle) is used to facilitate theevaluation in a test laminate that has a mottle rating lower than thescale of the standard set, such as lower than a rating of 1. A testlaminate that shows a shadowgraph projection similar to that of azero-mottle laminate is assessed to have a mottle rating of zero. Thetest laminate is prepared with two sheets of clear glass each having athickness of 2.3 mm (commercially available from Pittsburgh Glass Worksof Pennsylvania) and an interlayer. The interlayer typically has arandom rough surface R_(z) of about 35 to 40 microns and thickness of0.76 to 0.86 mm.

The mottle values provided herein were determined using a Clear MottleAnalyzer (CMA) that includes a xenon arc lamp, a sample holder, aprojection screen, and a digital camera. The xenon arc lamp is used toproject a shadowgraph of a laminated sample onto the screen and thecamera is configured to capture an image of the resulting shadowgraph.The image is then digitally analyzed using computer imaging software andcompared to images of previously-captured standard samples to determinethe mottle of the sample. A method of measuring mottle using a CMA isdescribed in detail in U.S. Patent Application Publication No. US2012-0133764.

Another parameter used to determine the optical performance istransparency, or percent visual transmittance (% T_(vis)), which ismeasured using a spectrophotometer, such as a HunterLab UltraScan EX, inaccordance with ASTM D1003, Procedure B using Illuminant C at anobserver angle of 2°. The values provided herein were obtained byanalyzing a glass laminate samples having an interlayer thickness ofabout 0.76 mm and a clear glass thickness of 2.3 mm (commerciallyavailable from Pittsburgh Glass Works of Pennsylvania). In someembodiments, the resin layers and interlayers of the present inventioncan have a percent visual transmittance of at least about 70, at leastabout 75, at least about 80, at least about 81, at least about 82, atleast about 83, at least about 84, at least about 85, at least about85.5, at least about 86, at least about 86.5, at least about 87, atleast about 87.5, at least about 88, or at least about 88.5 percent.More specifically, the resin layers and interlayers of the presentinvention have a % T_(vis) of greater than 85 for the interlayerscontaining only additives of ACAs, UV stabilizers, and antioxidant, orgreater than 80% for the interlayers containing additional additivessuch as pigments, IR absorbers or blockers as mentioned above. Polymerinterlayers containing high levels of pigments and/or dyes may havelower % T_(vis) values as desired, such as in mass pigmented or coloredpolymer interlayers.

In addition to exhibiting one or more optical properties within theranges above, the resin layers and interlayers described herein may alsoexhibit acoustic properties within a desirable range. In someembodiments, as discussed above, at least a portion of a resin layer orinterlayer may have a glass transition temperature of not more than 25,not more than about 20, not more than about 15, not more than about 10,not more than about 5, not more than about 0, not more than about −5, ornot more than about −10° C., which may facilitate acoustic performanceof the layer or interlayer. At the same time, at least a portion of thelayer or interlayer may have a glass transition temperature of at leastabout 26, at least about 30, at least about 35° C., which may facilitateimpact resistance properties and strength.

In some embodiments, a resin layer or interlayer according to thepresent invention may have a tan delta value of at least about 0.70. Tandelta is the ratio of the loss modulus (G″) in Pascals to the storagemodulus (G′) in Pascals of a specimen measured by Dynamic MechanicalThermal Analysis (DMTA). The DMTA is performed with an oscillationfrequency of 1 Hz under shear mode and a temperature sweep rate of 3°C./min. The peak value of the G″/G′ curve at the glass transitiontemperature is the tan delta value. Resin layers or interlayers asdescribed according to various embodiment herein can have a tan delta ofat least about 1.0, at least about 1.05, at least about 1.10, at leastabout 1.25, at least about 1.50, at least about 1.75, at least about2.0, or at least about 2.25.

Additionally, the resin layers and interlayers can have a damping lossfactor, or loss factor, of at least about 0.10, at least about 0.15, atleast about 0.17, at least about 0.20, at least about 0.25, at leastabout 0.27, at least about 0.30, at least about 0.33, or at least about0.35. Loss factor is measured by Mechanical Impedance Measurement asdescribed in ISO Standard 16940. A polymer sample is laminated betweentwo sheets of clear glass, each having a thickness of 2.3 mm, and isprepared to have a width of 25 mm and a length of 300 mm. The laminatedsample is then excited at the center point using a vibration shaker,commercially available from Brüel and Khær (Nærum, Netherlands) and animpedance head (Brüel and Kjær) is used to measure the force required toexcite the bar to vibrate and the velocity of the vibration. Theresultant transfer function is recorded on a National Instrument dataacquisition and analysis system and the loss factor at the firstvibration mode is calculated using the half power method. In someembodiments, when the RI balancing agent is a high RI plasticizer, thelayer or interlayer may have a loss factor greater than 0.25, greaterthan 0.27, greater than 0.30, or greater than 0.35 at 20° C., while, inother embodiments, when the RI balancing agent is a solid RI additive orresidues of at least one high RI aldehyde, the layer or interlayer mayhave a loss factor of at least about 0.10, at least about 0.15, at leastabout 0.20, at least about 0.25, or at least about 0.30° C. 20° C.

Similar to the resin blend of two distinct resins of the firstpoly(vinyl acetal) resin and the second poly(vinyl acetal) resin,blending two or more distinct resin layers or interlayers can oftenresult in the new resin layer(s) or interlayer(s) having unexpectedproperties and performance attributes. For example, a resin layer orinterlayer having lower residual hydroxyl content and lower glasstransition temperature may be blended with another resin layer orinterlayer having higher residual hydroxyl content and higher glasstransition temperature, resulting a new resin layer or interlayer havingsoft domains of lower glass transition temperature, which enhances itsacoustic performance, and stiff domains of higher glass transitiontemperature, which imparts enhanced processability, strength, and impactresistance to the resin layer or interlayer. Other example includesblending a single sheet interlayer and multilayer interlayer, blendingtwo multilayer interlayers, or blending one multilayer interlayer into aresin layer of another multilayer interlayer. In essence, the effectarising from blending two materials can also be achieved from blendingtwo or more resins, plasticizers, and other additives according to thecontents of the materials. As used herein, a “blend resin material” or“blend material” refers to the resin composition, resin layer orinterlayer to be blended into another resin composition, resin layer orinterlayer. In blending two resin layers or two interlayers, at leastone of the two materials to be blended can include the resin layer orinterlayer of the present invention. In other embodiments, bothmaterials can include the resin layers or interlayers of the presentinvention.

According to some embodiments, at least a portion of the resincompositions, layers, or interlayers described herein may compriseanother resins, layers, or interlayers. In some embodiments, at leastabout 0.5, at least about 1, at least about 5, at least about 10, atleast about 15, at least about 20, at least about 25, at least about 30,or at least about 50 percent of the total amount of resin in acomposition, layer, or interlayer can originate from a blend resinmaterial.

Often, when the type and/or amount of resins and plasticizers in theblend resin material differ substantially from the type and/or amount ofthe resin or plasticizer being produced, and into which the blend resinmaterial is being added, the optical performance, as determined by theclarity or haze, of the resulting resin composition, layer, orinterlayer that includes the blend resin material may be adverselyimpacted. According to embodiments of the present invention, resinlayers and interlayers that include higher levels of blend resinmaterial can be produced by utilizing one or more of the RI balancingagents discussed above.

When the RI balancing agent includes a high RI plasticizer, higheramounts of blend resin materials can be added to a process for producinga resin composition, layer, or interlayer described herein withoutreducing the clarity or increasing the haze of the final composition,layer, or interlayer. In some embodiments, the composition that includesblend materials can include a first poly(vinyl acetal) resin and asecond poly(vinyl acetal) resin, wherein one of the resins has aresidual hydroxyl content that can be at least 2 weight percent lowerthan the residual hydroxyl content of the other resin. Such acomposition may further include at least one high RI plasticizer havinga refractive index of 1.460, and, in some embodiments, more than 3percent of the combined amount of the first and second poly(vinylacetal) resins present in the composition, layer, or interlayer may haveoriginated from a blend composition, layer, or interlayer. Despite thedifference in residual hydroxyl contents of the first and secondpoly(vinyl acetal) resins, the composition that includes more than 0.5weight percent of blend resin materials may have a haze value of notmore than about 5, not more than about 4, not more than about 3, notmore than about 2, or not more than about 1, or not more than about 0.5.

The high RI plasticizer used as an RI balancing agent with blend resincompositions can have a refractive index within one or more of theranges described previously. The high RI plasticizer may be added duringproduction of the composition, layer, or interlayer along with the blendmaterial and/or at least a portion of the high RI plasticizer may bepresent in the blend resin material added to the process. Additionally,one or more other plasticizers may also be present in the resin materialbeing blended and/or in the resin composition, layer, or interlayerbeing produced, including, for example, those having a refractive indexless than about 1.450, less than about 1.445, or less than about 1.442,measured as described previously. In some embodiments, one or moreadditional high RI plasticizers may also be present in the blendmaterial and/or in the resin composition, layer, or interlayer intowhich the materials are being blended.

The resin composition that includes blended resin material as describedabove can be used to form layers and interlayers according to variousembodiments of the present invention. For example, the resin compositionincluding a blend resin material can be used to form a single monolithicinterlayer, or it may be used to form one or more layers of a multilayerinterlayer. When used in various layers and interlayers, additionalplasticizer may be added such that the total amount of plasticizerpresent in the resin layer or interlayer can be within the rangedescribed previously. Similarly, the glass transition temperature andrefractive indices of resin layers and interlayers formed from acomposition that includes a blend resin material may also be within theranges provided above. Additionally, resin layers and interlayers formedfrom a composition that includes blended materials may also exhibitacoustic properties as described previously and may be included in anyof the applications described below.

According to some embodiments, at least a portion of the resincompositions, layers, or interlayers described herein may comprise oneor more recycled resin materials, including, for example, recycledlayers or interlayers. As used herein, the term “recycled” means removedfrom and subsequently returned to a production line. Often, utilizingrecycled materials may adversely affect the optical performance of thefinal composition, layer, or interlayer, as determined by clarity orhaze, because of the different compositions and properties of thematerials being blended or combined. However, in some embodiments,layers or interlayers as described herein may include at least onerecycled resin material, while still exhibiting the same optical and/oracoustic properties as described herein. The type and/or amount ofrecycle resin material may fall within one or more of the rangesdescribed previously and the layer or interlayer may further include atleast one RI balancing agent. Additionally, the resin layers andinterlayers including recycled resin material may also have opticaland/or acoustic performance within one or more of the ranges describedbelow.

The resin compositions, layers, and interlayers described above may beproduced according to any suitable method. In various embodiments, themethod for producing these compositions, layers, and interlayers caninclude providing two or more poly(vinyl acetal) resins, blending atleast one resin with an RI balancing agent and, optionally, at least oneplasticizer or other additive, to form a blended composition, andforming a layer from the blended composition.

In some embodiments, the resins provided in the initial steps of themethod can be in the form of one or more poly(vinyl acetal) resins,while, in other embodiments, one or more resin precursors can also beprovided. In some embodiments, when two or more poly(vinyl acetal)resins are physically blended, the blending of the two resins cancomprise melt blending and may be performed at a temperature of at leastabout 140, at least about 150, at least about 180, at least about 200,at least about 250° C. In other embodiments, when the poly(vinyl acetal)resin components provided include resin precursors, the blending stepmay include reacting two or more aldehydes with a polyvinyl alcohol toprovide a single poly(vinyl acetal) resin having two or more aldehydemoieties. Additionally, a portion of the blending step can includeblending one or more of the resins with at least one plasticizer and/orwith one or more of the RI balancing agents described previously.

The resulting blended resins can then be formed into one or more resinlayers according to any suitable method. Exemplary methods of formingpolymer layers and interlayers can include, but are not limited to,solution casting, compression molding, injection molding, meltextrusion, melt blowing, and combinations thereof. Multilayerinterlayers including two or more resin layers may also be producedaccording to any suitable method such as, for example, co-extrusion,blown film, melt blowing, dip coating, solution coating, blade, paddle,air-knife, printing, powder coating, spray coating, and combinationsthereof. In various embodiments of the present invention, the layers orinterlayers may be formed by extrusion or co-extrusion. In an extrusionprocess, one or more thermoplastic polymers, plasticizers, and,optionally, at least one additive, including one or more RI balancingagents as described previously, can be pre-mixed and fed into anextrusion device. Other additives, such as ACAs, colorants, and UVinhibitors, which can be in liquid, powder, or pellet form, may also beused and may be mixed into the thermoplastic polymers or plasticizersprior to entering the extrusion device. These additives can beincorporated into the polymer resin and, by extension, the resultantpolymer sheet, thereby enhancing certain properties of the polymer layeror interlayer and its performance in the final multiple layer glasspanel or other end product.

In various embodiments, the thickness, or gauge, of the layers orinterlayers can be at least about 10, at least about 15, at least about20 mils and/or not more than about 100, not more than about 90, not morethan about 60, not more than about 50, or not more than about 35 mils,or it can be in the range of from about 10 to about 100, about 15 toabout 60, or about 20 to about 35 mils. In millimeters, the thickness ofthe polymer layers or interlayers can be at least about 0.25, at leastabout 0.38, at least about 0.51 mm and/or not more than about 2.54, notmore than about 2.29, not more than about 1.52, or not more than about0.89 mm, or in the range of from about 0.25 to about 2.54 mm, about 0.38to about 1.52 mm, or about 0.51 to about 0.89 mm. In some embodiments,the resin layers or interlayers can comprise flat polymer layers havingsubstantially the same thickness along the length, or longest dimension,and/or width, or second longest dimension, of the sheet, while, in otherembodiments, one or more layers of a multilayer interlayer, for example,can be tapered or can have a wedge-shaped profile, such that thethickness of the interlayer changes along the length and/or width of thesheet, such that one edge of the layer or interlayer has a thicknessgreater than the other. When the interlayer is a multilayer interlayer,at least one, at least two, or at least three of the layers of theinterlayer can comprise at least one tapered zone. When the interlayeris a monolithic interlayer, the polymer sheet can be flat or may includeat least one tapered zone. Tapered interlayers may be useful in, forexample, heads-up-display (HUD) panels in automotive and aircraftapplications.

Turning now to FIGS. 1 through 8, several embodiments of taperedinterlayers according to the present invention are provided. FIG. 1 is across-sectional view of an exemplary tapered interlayer that includes atapered zone of varying thickness. As shown in FIG. 1, the tapered zonehas a minimum thickness, T_(min), measured at a first boundary of thetapered zone and a maximum thickness, T_(max), measured at a secondboundary of the tapered zone. In certain embodiments, T_(min) can be atleast about 0.25, at least about 0.40, or at least about 60 millimeters(mm) and/or not more than 1.2, not more than about 1.1, or not more thanabout 1.0 mm. Further, T_(min) can be in the range of 0.25 to 1.2 mm,0.4 to 1.1 mm, or 0.60 to 1.0 mm. In certain embodiments, T_(max) can beat least about 0.38, at least about 0.53, or at least about 0.76 mmand/or not more than 2.2, not more than about 2.1, or not more thanabout 2.0 mm. Further, T_(max) can be in the range of 0.38 to 2.2 mm,0.53 to 2.1 mm, or 0.76 to 2.0 mm. In certain embodiments, thedifference between T_(max) and T_(min) can be at least about 0.13, atleast about 0.15, at least about 0.2, at least about 0.25, at leastabout 0.3, at least about 0.35, at least about 0.4 mm and/or not morethan 1.2, not more than about 0.9, not more than about 0.85, not morethan about 0.8, not more than about 0.75, not more than about 0.7, notmore than about 0.65, or not more than about 0.6 mm. Further, thedifference between T_(max) and T_(min) can be in the range of 0.13 to1.2 mm, 0.25 to 0.75 mm, or 0.4 to 0.6 mm. In certain embodiments, thedistance between the first and second boundaries of the tapered zone(i.e. the “tapered zone width”) can be at least about 5, at least about10, at least about 15, at least about 20, or at least about 30centimeters (cm) and/or not more than about 200, not more than about150, not more than about 125, not more than about 100 or not more thanabout 75 cm. Further, the tapered zone width can be in the range of 5 to200 cm, 15 to 125 cm, or 30 to 75 cm.

As shown in FIG. 1, the tapered interlayer includes opposite first andsecond outer terminal edges. In certain embodiments, the distancebetween the first and second outer terminal edges (i.e., the “interlayerwidth”) can be at least about 20, at least about 40, or at least about60 cm and/or not more than about 400, not more than about 200, or notmore than about 100 cm. Further the interlayer width can be in the rangeof 20 to 400 cm, 40 to 200 cm, or 60 to 100 cm. In the embodimentdepicted in FIG. 1, the first and second boundaries of the tapered zoneare spaced inwardly from the first and second outer terminal edges ofthe interlayer. In such embodiments, only a portion of the interlayer istapered. When the tapered zone forms only a portion of the interlayer,the ratio of the interlayer width to the tapered zone width can be atleast about 0.05:1, at least about 0.1:1, at least about 0.2:1, at leastabout 0.3:1, at least about 0.4:1 at least about 0.5:1, at least about0.6:1, or at least about 0.7:1 and/or not more than about 1:1, not morethan about 0.95:1, not more than about 0.9:1, not more than about 0.8:1,or not more than about 0.7:1. Further, the ratio of interlayer width tothe tapered zone width can be in the range of 0.05:1 to 1:1 or 0.3:1 to0.9:1. In an alternative embodiment, discussed below, the entireinterlayer is tapered. When the entire interlayer is tapered, thetapered zone width is equal to the interlayer width and the first andsecond boundaries of the tapered zone are located at the first andsecond terminal edges, respectively.

As illustrated in FIG. 1, the tapered zone of the interlayer has a wedgeangle, which is defined as the angle formed between a first referenceline extending through two points of the interlayer where the first andsecond tapered zone boundaries intersect a first (upper) surface of theinterlayer and a second reference line extending through two pointswhere the first and second tapered zone boundaries intersect a second(lower) surface of the interlayer. In certain embodiments, the wedgeangle of the tapered zone can be at least about 0.13, at least about0.15, at least about 0.2, at least about 0.25, at least about 0.3, atleast about 0.35, at least about 0.4 milliradians (mrad) and/or not morethan about 1.2, not more than about 1.0, not more than about 0.9, notmore than about 0.85, not more than about 0.8, not more than about 0.75,not more than about 0.7, not more than about 0.65, or not more thanabout 0.6 mrad. Further, the wedge angle of the tapered zone can be inthe range of 0.13 to 1.2 mrad, 0.25 to 0.75 mrad, or 0.4 to 0.6 mrad.

When the first and second surfaces of the tapered zone are each planar,the wedge angle of the tapered zone is simply the angle between thefirst (upper) and second (lower) surfaces. However, as discussed infurther detail below, in certain embodiments, the tapered zone caninclude at least one variable angle zone having a curved thicknessprofile and a continuously varying wedge angle. Further, in certainembodiments, the tapered zone can include two or more constant anglezones, where the constant angle zones each have a linear thicknessprofile, but at least two of the constant angle zones have differentwedge angles.

FIGS. 2-7 illustrate various tapered interlayers configured accordingembodiments of the present invention. FIG. 2 depicts an interlayer 20that includes a tapered zone 22 extending entirely from a first terminaledge 24 a of the interlayer 20 to a second terminal edge 24 b of theinterlayer 20. In this configuration, the first and second boundaries ofthe tapered zone are located at the first and second terminal edges 24a,b of the interlayer. The entire tapered zone 22 of the interlayer 20depicted in FIG. 2 has a constant wedge angle Θ that is simply the angleformed between the planar first (upper) and second (lower) planarsurfaces of the interlayer 20.

FIG. 3 illustrates an interlayer 30 that includes a tapered zone 32 anda flat edge zone 33. The first boundary 35 a of the tapered zone 32 islocated at the first terminal edge 34 a of the interlayer 30, while thesecond boundary 35 b of the tapered zone 32 is located where the taperedzone 32 and the flat edge zone 33 meet. The tapered zone 32 includes aconstant angle zone 36 and a variable angle zone 37. The constant anglezone 36 has a linear thickness profile and a constant wedge angle,Θ_(c), while the variable angle zone 37 has a curved thickness profileand a continuously varying wedge angle. The starting wedge angle of thevariable angle zone 37 is equal to the constant wedge angle Θ_(c) andthe ending wedge angle of the variable angle zone 37 is zero. Theinterlayer 30 depicted in FIG. 3 has a constant wedge angle Θ_(c) thatis greater than the overall wedge angle of the entire tapered zone 32.

FIG. 4 illustrates an interlayer 40 that includes a tapered zone 42located between first and second flat edge zones 43 a,b. The firstboundary 45 a of the tapered zone 42 is located where the tapered zone42 and the first flat edge zone 43 a meet, while the second boundary 45b of the tapered zone 42 is located where the tapered zone 42 and thesecond flat edge zone 43 b meet. The tapered zone 42 includes a constantangle zone 46 located between first and second variable angle zones 47a,b. The first variable angle zone 47 a forms a transition zone betweenthe first flat edge zone 43 a and the constant angle zone 46. The secondvariable angle zone 47 b forms a transition zone between the second flatedge zone 43 b and the constant angle zone 46. The constant angle zone46 has a linear thickness profile and a constant wedge angle, Θ_(c),while the first and second variable angle zones 47 a,b have curvedthickness profiles and continuously varying wedge angles. The startingwedge angle of the first variable angle zone 47 a is equal to zero andthe ending wedge angle of the first variable angle zone 47 b is equal tothe constant wedge angle Θ_(c). The starting wedge angle of the secondvariable angle zone 47 b is equal to the constant wedge angle Θ_(c) andthe ending wedge angle of the second variable angle zone 47 b is zero.The interlayer 40 depicted in FIG. 4 has a constant wedge angle Θ_(c)that is greater than the overall wedge angle of the entire tapered zone42.

FIG. 5 illustrates an interlayer 50 that includes a tapered zone 52located between first and second flat edge zones 53 a,b. The taperedzone 52 of the interlayer 50 does not include a constant angle zone.Rather, the entire tapered zone 52 of the interlayer 50 is a variableangle zone having a curved thickness profile and a continuously varyingwedge angle. As described above, the overall wedge angle, Θ, of thetapered zone 52 is measured as the angle between a first reference line“A” extending through the two points where the first and secondboundaries 55 a,b of the tapered zone 52 meet the first (upper) surfaceof the interlayer 50 and a second reference line “B” extending throughthe two points where the first and second boundaries 55 a,b of thetapered zone 52 meet the second (lower) surface of the interlayer 50.However, within the tapered zone 52, the curved thickness profileprovides an infinite number of wedge angles, which can be greater than,less than, or equal to the overall wedge angle Θ of the entire taperedzone 52.

FIG. 6 illustrates an interlayer 60 that does not include any flat endportions. Rather, the tapered zone 62 of the interlayer 60 forms theentire interlayer 60. Thus, the first and second boundaries 65 a,b ofthe tapered zone 60 are located at the first and second terminal edges64 a,b of the interlayer 60. The tapered zone 62 of the interlayer 60includes first, second, and third constant angle zones 46 a,b,c separateby first and second variable angle zones 47 a,b. The first, second, andthird constant angle zones 46 a,b,c each have a linear thickness profileand each have unique first, second, and third constant wedge angles,Θ_(ca), Θ_(c2), Θ_(c3), respectively The first variable angle zone 47 aacts as a transition zone between the first and second constant anglezones 46 a,b. The second variable angle zone 47 b acts as a transitionzone between the second and third constant angle zones 46 b,c. Asdiscussed above, the overall wedge angle, Θ, of the tapered zone 62 ismeasured as the angle between a first reference line “A” and a secondreference line “B.” The first constant wedge angle Θ_(c1) is less thanthe overall wedge angle Θ of the tapered zone 62. The second constantwedge angle Θ_(c2) is greater the overall wedge angle Θ of the taperedzone 62. The third constant wedge angle Θ_(c3) is less than the overallwedge angle Θ of the tapered zone 62. The wedge angle of the firstvariable angle zone 47 a continuously increases from the first constantwedge angle Θ_(c1) to the second constant wedge angle, Θ_(c2). The wedgeangle of the second variable angle zone 47 b continuously decreases fromthe second constant wedge angle Θ_(c2) to the third wedge angle Θ_(c3).

FIG. 7 illustrates an interlayer 70 that includes a tapered zone 72located between first and second flat edge zones 73 a,b. The first andsecond boundaries 75 a,b of the tapered zone 72 are spaced inwardly fromthe first and second outer edges 74 a,b of the interlayer 70. Thetapered zone 72 of the interlayer 70 includes first, second, third, andfourth variable angle zones 77 a,b,c,d and first, second, and thirdconstant angle zones 76 a,b,c. The first variable angle zone 77 a actsas a transition zone between the first flat edge zone 73 a and the firstconstant angle zone 76 a. The second variable angle zone 77 b acts as atransition zone between the first constant angle zone 76 a and thesecond constant angle zone 76 b. The third variable angle zone 77 c actsas a transition zone between the second constant angle zone 76 b and thethird constant angle zone 76 c. The fourth variable angle zone 77 d actsas a transition zone between the third constant angle zone 76 c and thesecond flat edge zone 73 b. The first, second, and third constant anglezones 76 a,b,c each have a linear thickness profile and each have uniquefirst, second, and third constant wedge angles, Θ_(ca), Θ_(c2), Θ_(c3),respectively As discussed above, the first, second, third, and fourthvariable angle zones 77 a,b,c,d have wedge angles that continuouslytransition from the wedge angle of the constant angle zone on one sideof the variable angle zone 77 to the wedge angle of the constant anglezone on the other side of the variable angle zone 77.

As discussed above, the tapered interlayer can include one or moreconstant angle tapered zones, each having a width that is less than theoverall width of the entire tapered zone and each having a wedge anglethat is the same as or different than the overall wedge angle of theentire tapered zone. For example, the tapered zone can include one, two,three, four, five, or more constant angle tapered zones. When multipleconstant angle tapered zones are employed, the constant angle taperedzones can be separated from one another by variable angle tapered zonesthat serve to transition between adjacent constant angle tapered zones.

In certain embodiments, the width of each constant angle tapered zonecan be at least about 2, at least about 5, at least about 10, at leastabout 15, or at least about 20 cm and/or not more than about 150, notmore than about 100, or not more than about 50 cm. In certainembodiments, the ratio of the width of each constant angle tapered zoneto the overall width of the entire tapered zone can be at least about0.1:1, at least about 0.2:1, at least about 0.3:1 or at least about0.4:1 and/or not more than about 0.9:1, not more than about 0.8:1, notmore than about 0.7:1, not more than about 0.6:1, or not more than about0.5:1.

In certain embodiments, the wedge angle of each constant angle taperedzone can be at least about 0.13, at least about 0.15, at least about0.2, at least about 0.25, at least about 0.3, at least about 0.35, atleast about 0.4 mrad and/or not more than about 1.2, not more than about1.0, not more than about 0.9, not more than about 0.85, not more thanabout 0.8, not more than about 0.75, not more than about 0.7, not morethan about 0.65, or not more than about 0.6 mrad. Further, the wedgeangle of each constant angle tapered zone can be in the range of 0.13 to1.2 mrad, 0.25 to 0.75 mrad, or 0.4 to 0.6 mrad. In certain embodiments,the wedge angle of at least one constant angle tapered zone is at leastabout 0.01, at least about 0.05, at least about 0.1, at least about 0.2,at least about 0.3, or at least about 0.4 mrad greater than the overallwedge angle of the entire tapered zone. In certain embodiments, thewedge angle of at least one constant angle tapered zone is at leastabout 0.01, at least about 0.05, at least about 0.1, at least about 0.2,at least about 0.3, or at least about 0.4 mrad less than the overallwedge angle of the entire tapered zone. In certain embodiments, thewedge angle of at least one constant angle tapered zone is not more thanabout 0.4, not more than about 0.3, not more than about 0.2, not morethan about 0.1, not more than about 0.05, or not more than about 0.01mrad greater than the overall wedge angle of the entire tapered zone. Incertain embodiments, the wedge angle of at least one constant angletapered zone is not more than about 0.4, not more than about 0.3, notmore than about 0.2, not more than about 0.1, not more than about 0.05,or not more than about 0.01 mrad less than the overall wedge angle ofthe entire tapered zone.

FIGS. 8a and 8b illustrate an interlayer 80 that is similar in thicknessprofile to the interlayer 30 of FIG. 3. The interlayer 80 of FIGS. 8aand 8b is configured for use in a vehicle windshield by fixing theinterlayer between two sheets of glass. As depicted in FIG. 8a , thefirst terminal edge 84 a of the interlayer 80 can be located at thebottom of the windshield, while the second terminal edge 84 b of theinterlayer 80 can be located at the top of the windshield. The taperedzone 82 of the interlayer 80 is positioned in an area of the windshieldwhere a heads-up display is to be located. The tapered zone 82 ofinterlayer 80 includes a constant angle zone 86 and a variable anglezone 87. As depicted in FIG. 8a , in certain embodiments, the taperedzone 82 extends entirely across the interlayer 80 between a first sideedge 88 a and a second side edge 88 b of the interlayer 80. FIG. 8b ,which is similar to FIG. 3, shows the thickness profile of theinterlayer 80 between the bottom of the windshield and the top of thewindshield.

Although not illustrated in the drawings, it should be understood thatin certain embodiments, the tapered interlayer can be a multilayeredinterlayer. When the tapered interlayer comprises multiple individuallayers, all of the individual layers can be tapered, part of theindividual layers can be tapered, or only one of the individual layerscan be tapered. Further, in certain embodiments the glass transitiontemperatures of the individual layers can be different than another. Forexample, in one embodiment, the interlayer includes a tapered middlelayer having a lower glass transition temperature than two tapered outerlayers of the interlayer, where the glass transition temperature of oneor both of the outer layers exceeds the glass transition temperature ofthe middle layer by at least about 10, at least about 20, at least about30, at least about 40, or at least about 50° C.

In some embodiments, the resin layers or interlayers can comprise flatpolymer layers having substantially the same thickness along the length,or longest dimension, and/or width, or second longest dimension, of thesheet, while, in other embodiments, one or more layers of a multilayerinterlayer, for example, can be wedge-shaped or can have a wedge-shapedprofile, such that the thickness of the interlayer changes along thelength and/or width of the sheet, such that one edge of the layer orinterlayer has a thickness greater than the other. When the interlayeris a multilayer interlayer, at least one, at least two, or at leastthree of the layers of the interlayer can be wedge-shaped. When theinterlayer is a monolithic interlayer, the polymer sheet can be flat orwedge shaped. Wedge-shaped interlayers may be useful in, for example,heads-up-display (HUD) panels in automotive and aircraft applications.

The resin compositions, layers, and interlayers according to embodimentsof the present invention may be utilized in a multiple layer panel thatcomprises a resin layer or interlayer and at least one rigid substrate.Any suitable rigid substrate may be used and in some embodiments may beselected from the group consisting of glass, polycarbonate, biaxiallyoriented PET, copolyesters, acrylic, and combinations thereof. When therigid substrate includes glass, the glass can be selected from the grouplisted previously. When the rigid substrate includes a polymericmaterial, the polymeric material may or may not include a hard coatsurface layer. In some embodiments, the multilayer panels include a pairof rigid substrates with the resin interlayer disposed therebetween. Thepanels can be used for a variety of end use applications, including, forexample, for automotive windshields and windows, aircraft windshieldsand windows, panels for various transportation applications such asmarine applications, rail applications, etc., structural architecturalpanels such as windows, doors, stairs, walkways, balusters, decorativearchitectural panels, weather-resistant panels, such as hurricane glassor tornado glass, ballistic panels, and other similar applications.

When laminating the resin layers or interlayers between two rigidsubstrates, such as glass, the process can include at least thefollowing steps: (1) assembly of the two substrates and the interlayer;(2) heating the assembly via an IR radiant or convective device for afirst, short period of time; (3) passing the assembly into a pressurenip roll for the first de-airing; (4) heating the assembly for a shortperiod of time to about 60° C. to about 120° C. to give the assemblyenough temporary adhesion to seal the edge of the interlayer; (5)passing the assembly into a second pressure nip roll to further seal theedge of the interlayer and allow further handling; and (6) autoclavingthe assembly at temperature between 135° C. and 150° C. and pressuresbetween 150 psig and 200 psig for about 30 to 90 minutes. Other methodsfor de-airing the interlayer-glass interface, as described according tosome embodiments in steps (2) through (5) above include vacuum bag andvacuum ring processes, and both may also be used to form interlayers ofthe present invention as described herein.

In some embodiments, the multiple layer panel may include at least onepolymer film disposed on the layer or interlayer, forming a multiplelayer panel referred to as a “bilayer.” In some embodiments, theinterlayer utilized in a bilayer may include a multilayer interlayer,while, in other embodiments, a monolithic interlayer may be used. Theuse of a polymer film in multiple layer panels as described herein mayenhance the optical character of the final panel, while also providingother performance improvements, such as infrared absorption. Polymerfilms differ from polymer layers or interlayers in that the films alonedo not provide the necessary penetration resistance and glass retentionproperties. The polymer film can also be thinner than the sheet, and mayhave a thickness in the range of from 0.001 to 0.25 mm. Poly(ethyleneterephthalate) (“PET”) is one example of a material used to form thepolymer film.

The following examples are intended to be illustrative of the presentinvention in order to teach one of ordinary skill in the art to make anduse the invention and are not intended to limit the scope of theinvention in any way.

EXAMPLES

The following Examples describe the preparation of several resincompositions, layers, and interlayers that include various poly(vinylacetal) reins. As described below, several tests performed on many ofthe compositions, layers, and interlayers were used to evaluate theacoustic and optical properties of several comparative and inventivematerials.

Example 1: Preparation of High Refractive Index Poly(Vinyl Acetal)Resins

Several comparative poly(vinyl acetal) resins, referred to asComparative Resins CR-1 through CR-12 in Table 2 below, were prepared byacetalizing polyvinyl alcohol with one or more aldehydes includingn-butyraldehyde (nBuCHO; RI=1.377), iso-butyraldehyde (iBuCHO;RI=1.374), and 2-ethylhexyl aldehyde (2EHCHO; RI=1.414). The compositionof the resulting resins were measured using either the ASTM D1396 orFT-IR/SEC method described in detail previously. The refractive indexand glass transition temperature (T_(g)) of several of the resins wasalso measured according to the methods described previously, and theresults are provided in Table 2, below.

TABLE 2 Properties of Several Comparative Poly(vinyl acetal) ResinsResi- Resin dual Resi- Residual Residual Residual Refrac- Hydrox- dualPolyvinyl Polyvinyl Polyvinyl tive yl Acetate nBuCHO iBuCHO 2EHCHO IndexResin (wt %) (wt %) (wt %) (wt %) (wt %) (nD25) CR-1 21 1 78 — — 1.491CR-2 19 1 80 — — 1.490 CR-3 19 1 46 — 34 1.489 CR-4 16 1 83 — — 1.488CR-5 15 1 39 — 45 1.487 CR-6 13 1 86 — — 1.486 CR-7 12 18 70 — — 1.481CR-8 12 12 76 — — nd CR-9 12 10 78 — — 1.483 CR-10 11 1 88 — — 1.485CR-11 12 1 — 88 — nd CR-12 13 1 — 86 — nd nd = not determined

Additionally, several poly(vinyl acetal) resins according to embodimentsof the present invention were also prepared in a similar manner. Theseinventive resins, referred to as Disclosed Resins DR-1 through DR-21 inTable 3, were formed by acetalizing polyvinyl alcohol with mixtures ofn-butyraldehyde and various high refractive index aldehydes, includingbenzaldehyde (BzCHO RI=1.545), cinnamaldehyde (CCHO; RI=1.620),4-chlorobenzaldehyde (4-ClBzCHO; RI=1.5850), 2-phenylpropionaldehyde(2PHPrCHO; RI=1.517), and hydrocinnamaldehyde (HCCHO; RI=1.523). Therefractive index of several of the Disclosed Resins was also determinedand the results are summarized in Table 3, below.

TABLE 3 Properties of Disclosed Resins Resin Residual Residual AldehydeHCCHO/ CCHO/ 2PhPrCHO/ BzCHO/ 4ClBzCHO/ Refractive Hydroxyl AcetateComponent BuCHO BuCHO BuCHO BuCHO BuCHO HCCHO/ Index Resin (wt %) (wt %)(wt %) (mol/mol) (mol/mol) (mol/mol) (mol/mol) mol/mol) iBuCHO (nD25)DR-1 11 1 88  5/95 — — — — — 1.496 DR-2 11 1 88 10/90 — — — — — 1.500DR-3 11 1 88 15/85 — — — — — 1.504 DR-4 11 1 88 20/80 — — — — — 1.510DR-5 11 1 88 25/75 — — — — — 1.511 DR-6 11 1 88 50/50 — — — — — 1.528DR-7 11 1 88 100/0  — — — — — 1.552 DR-8 19 1 80 10/90 — — — — — nd DR-919 1 80 25/75 — — — — — nd DR- 19 1 80 50/50 — — — — — nd 10 DR- 19 1 80100/0  — — — — — nd 11 DR- 12 18 70 25/75 — — — — — nd 12 DR- 12 10 7825/75 — — — — — nd 13 DR- 17 1 82 — 25/75 — — — — 1.507 14 DR- 15 1 84 —— 25/75 — — — 1.505 15 DR- 14 1 85 — — 25/75 — — — 1.503 16 DR- 18 1 81— — — 25/75 — — 1.507 17 DR- 14 1 85 — — — 25/75 — — 1.501 18 DR- 20 179 — — — — 25/75 — 1.507 19 DR- 14 1 85 — — — — 25/75 — 1.509 20 DR- 111 88 — — — — — 25/75 nd 21 nd = not determined

As shown in Tables 2 and 3, above, polyvinyl acetal resins comprisingresidues of at least one high refractive index aldehyde, including thoselisted above, tend to exhibit higher refractive indices than thosecomprising residues of aldehydes such as n-butyraldehyde,iso-butyraldehyde, and 2-ethylhexyl aldehyde.

Example 2: Preparation of High Refractive Index Resin Interlayers

Several Comparative and Disclosed Interlayers were formed by mixing andmelt blending several of the Comparative Resins listed in Table 2 andseveral of the Disclosed Resins listed in Table 3 above, with varyingamounts of the plasticizer triethylene glycol bis(2-ethylhexanoate)(3GEH). The composition, refractive index, and glass transitiontemperature of each of the resulting interlayers, referred to asComparative Interlayers CL-1 through CL-14 and Disclosed InterlayersDL-1 through DL-26, were measured as described previously, and theresults are respectively summarized in Tables 4 and 5, below.

TABLE 4 Properties of Several Comparative Interlayers Refractive IndexT_(g) Interlayer Resin Plasticizer (phr) (nD25) (° C.) CL-1 CR-1 341.478 36 CL-2 CR-2 38 1.477 30 CL-3 CR-3 38 1.475 28 CL-4 CR-4 50 1.47217 CL-5 CR-4 30 1.477 30 CL-6 CR-5 75 1.468 6 CL-7 CR-6 75 1.467 2 CL-8CR-7 75 1.464 −4 CL-9 CR-8 75 1.466 −3 CL-10 CR-9 75 1.465 −3 CL-11CR-10 75 1.466 −2 CL-12 CR-10 50 1.47 12 CL-13 CR-11 75 nd nd CL-14CR-12 75 nd nd nd = not determined

TABLE 5 Properties of Several Disclosed Interlayers Sheet RefractivePlasticizer Index T_(g) Interlayer Resin content (phr) (nD25) (° C.)DL-1 DR-1 75 1.473 1 DL-2 DR-1 50 1.479 12 DL-3 DR-2 75 1.475 0 DL-4DR-3 75 1.477 0 DL-5 DR-4 75 1.480 1 DL-6 DR-5 75 1.482 1 DL-7 DR-6 751.490 2 DL-8 DR-7 75 1.506 3 DL-9 DR-14 75 1.480 12 DL-10 DR-15 75 1.47811 DL-11 DR-16 75 1.477 7 DL-12 DR-17 75 1.480 22 DL-13 DR-18 75 1.47612 DL-14 DR-19 75 1.480 17 DL-15 DR-20 75 1.479 12 DL-16 DR-12 75 nd ndDL-17 DR-13 75 nd nd DL-18 DR-21 75 nd nd DL-19 DR-8 38 1.477 30 DL-20DR-9 38 1.487 nd DL-21 DR-10 38 1.501 nd DL-22 DR-11 38 1.525 nd DL-23DR-5 38 nd nd DL-24 DR-5 50 1.488 nd DL-25 DR-5 60 1.484 2 DL-26 DR-7 38nd nd nd = not determined

As shown in Tables 4 and 5, above, Disclosed Interlayers utilizinghigher refractive index Disclosed Resins from Table 3 exhibit higherrefractive indices than Comparative Interlayers formulated with lowerrefractive index resins, such as the Comparative Resins listed in Table2. Additionally, as shown by comparison of Disclosed Interlayers DL-1and DL-2 and DL-6 and DL-23 through DL-25, the amount of plasticizerused to form an interlayer affects both the glass transition temperatureand refractive index of the layer, although not necessarily to the sameextent for all resins. For example, as shown by the comparison of DL-1(75 phr 3GEH; Disclosed Resin 1) and DL-2 (50 phr 3GEH; Disclosed Resin1), reducing the amount of plasticizer by about 33 percent increases theglass transition temperature of the interlayer by 11° C. (from 1° C. to12° C.), but only increases the refractive index by 0.006 (from 1.473 to1.479). However, as shown by the comparison of DL-25 (60 phr 3GEH;Disclosed Resin 5) and DL-6 (75 phr of 3GEH; Disclosed Resin 5),reducing the plasticizer content in layers formed by this resinincreases the glass transition temperature by only 1° C. (from 1° C. to2° C.), while increasing the refractive index by 0.004 (from 1.484 to1.488).

Example 3: Preparation of Interlayers Using High Refractive Index Resins

Several of the Comparative and Disclosed Interlayers formed in Example 2and respectively summarized in Tables 4 and 5, above, were used tocreate several Comparative and Disclosed Multilayer Interlayers. Eachmultilayer interlayer included a pair of outer “skin” layers, having atotal thickness of 28 mils, sandwiching an inner “core” layer having athickness of 5 mils, usually formed of a resin having a lower residualhydroxyl content. The composition and several properties of theinterlayers including refractive index, glass transition temperature,mottle, and loss factor, were measured as described above, and theresults for the Comparative Multilayer Interlayers (CI-1 to CI-16) andDisclosed Multilayer Interlayers (DI-1 to DI-29) are summarized inTables 6 and 7, below.

TABLE 6 Properties of Several Comparative Multilayer Interlayers ΔRefractive Refractive Index Index of Loss Resin Layer T_(g) (° C.)Refractive Index (Skin − Interlayer Factor at Interlayer Skin 1 CoreSkin 2 Skin 1 Core Skin 2 Skin 1 Core Skin 2 Core) (nD25) Mottle 20° C.CI-1 CL-2 CL-7 CL-2 30 2 30 1.477 1.467 1.477 0.010 1.475 4 0.29 CI-2CL-2 CL-11 CL-2 30 −2 30 1.477 1.466 1.477 0.011 1.475 5 0.33 CI-3 CL-2CL-8 CL-2 30 −4 30 1.477 1.464 1.477 0.013 1.475 5 nd CI-4 CL-1 CL-9CL-1 36 −3 36 1.478 1.466 1.478 0.012 1.477 5 nd CI-5 CL-1 CL-8 CL-1 36−4 36 1.478 1.464 1.478 0.014 nd 5 0.36 CI-6 CL-2 CL-9 CL-2 30 −3 301.477 1.466 1.477 0.011 nd 5 nd CI-7 CL-1 CL-11 CL-1 36 −2 36 1.4781.466 1.478 0.012 1.477 5 0.35 CI-8 CL-2 CL-10 CL-2 30 −3 30 1.477 1.4651.477 0.012 nd 5 0.31 CI-9 CL-1 CL-7 CL-1 36 2 36 1.478 1.467 1.4780.011 nd 5 nd CI-10 CL-1 CL-10 CL-1 36 −3 36 1.478 1.465 1.478 0.013 nd5 nd CI-11 CL-2 CL-13 CL-2 30 nd 30 nd nd nd nd nd >5 nd CI-12 CL-2CL-14 CL-2 30 nd 30 nd nd nd nd nd >5 nd CI-13 CL-1 CL-13 CL-1 36 nd 36nd nd nd nd nd >5 nd CI-14 CL-1 CL-14 CL-1 36 nd 36 nd nd nd nd nd >5 ndCI-15 CL-2 DL-7 CL-2 30 2 30 1.477 1.490 1.477 −0.013 1.479 >5 nd CI-16CL-2 DL-8 CL-2 30 3 30 1.477 1.506 1.477 −0.029 1.481 >5 nd nd = notdetermined

TABLE 7 Properties of Some Disclosed Multilayer Interlayers Δ RefractiveRefractive Index Index Refractive Resin Layer T_(g) (° C.) (nD25) (Skin− Index of Interlayer Skin 1 Core Skin 2 Skin 1 Core Skin 2 Skin 1 CoreSkin 2 Core) Interlayer Mottle DI-1 CL-2 DL-1 CL-2 30 1 30 1.477 1.4731.477 0.004 1.476 1 DI-2 CL-2 DL-4 CL-2 30 0 30 1.477 1.477 1.477 0.0001.477 1 DI-3 CL-5 DL-6 CL-5 30 1 30 1.477 1.482 1.477 −0.005 1.478 ndDI-4 CL-2 DL-6 CL-2 30 1 30 1.477 1.482 1.477 −0.005 nd <1 DI-5 CL-1DL-6 CL-1 36 1 36 1.478 1.482 1.478 −0.004 nd <1 DI-6 CL-2 DL-3 CL-2 300 30 1.477 1.475 1.477 0.002 nd <1 DI-7 CL-2 DL-5 CL-2 30 1 30 1.4771.480 1.477 −0.003 nd <1 DI-8 CL-2 DL-6 CL-1 30 1 36 1.477 1.482 1.478−0.005 nd <1 DI-9 CL-2 DL-6 CL-5 30 1 30 1.477 1.482 1.477 −0.005 nd <1DI-10 CL-2 DL-16 CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-11 CL-2 DL-17CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-12 CL-1 DL-16 CL-1 36 nd 361.478 nd 1.478 nd nd <1 DI-13 CL-1 DL-17 CL-1 36 nd 36 1.478 nd 1.478 ndnd <1 DI-14 CL-2 DL-18 CL-2 30 nd 30 1.477 nd 1.477 nd nd <1 DI-15 CL-1DL-18 CL-1 36 nd 36 1.478 nd 1.478 nd nd <1 DI-16 DL-19 DL-24 DL-19 30 130 1.477 1.488 1.477 −0.005 1.478 <1 DI-17 CL-2 DL-9 CL-2 30 12 30 1.4771.480 1.477 −0.003 nd <1 DI-18 CL-2 DL-10 CL-2 30 11 30 1.477 1.4781.477 −0.001 nd <1 DI-19 CL-2 DL-11 CL-2 30 7 30 1.477 1.477 1.477 0.000nd <1 DI-20 CL-2 DL-12 CL-2 30 22 30 1.477 1.480 1.477 −0.003 nd <1DI-21 CL-2 DL-13 CL-2 30 12 30 1.477 1.476 1.477 0.001 nd <1 DI-22 CL-2DL-14 CL-2 30 17 30 1.477 1.480 1.477 −0.003 nd <1 DI-23 CL-2 DL-15 CL-230 12 30 1.477 1.479 1.477 −0.002 nd <1 DI-24 DL-20 DL-7 DL-20 nd 2 nd1.487 1.490 1.487 −0.003 nd <1 DI-25 DL-21 DL-7 DL-21 nd 2 nd 1.5011.490 1.501 −0.011 nd >5 DI-26 DL-22 DL-7 DL-22 nd 2 nd 1.525 1.4901.525 −0.035 nd >5 DI-27 DL-20 DL-8 DL-20 nd 3 nd 1.487 1.506 1.487−0.009 nd 3 DI-28 DL-21 DL-8 DL-21 nd 3 nd 1.501 1.506 1.501 −0.005 nd<1 DI-29 DL-22 DL-8 DL-22 nd 3 nd 1.525 1.506 1.525 −0.019 nd >5 nd =not determined

As shown in Table 6, above, interlayers formed from skin and core layershaving refractive index differences of 0.010 or more exhibited opticaldefects, as indicated by the mottle values greater than 5. As shown inTable 7, however, interlayers formed from skin and core layers havingrefractive index differences of less than 0.010 exhibited low mottlevalues of 1 or less. Additionally, as shown in Table 7, such low mottlevalues were achievable by interlayers having a core layer with a higheror lower refractive index than the skin layer, as long as the absolutevalue of the difference between the refractive indices of adjacentlayers was less than 0.010. Also as shown in Table 7, interlayers formedfrom skin and core layers both having high RI aldehyde residues andhaving refractive index differences of greater than 0.010 exhibited highmottle values of 5 or greater.

Example 4: Stability of Multilayer Interlayers

Two Comparative Multilayer Interlayers, CI-2 and CI-7, and two DisclosedMultilayer Interlayers, DI-4 and DI-5, prepared as described in Examples1-3 above, were tested to determine the relative stability of theinterlayers over time. Net plasticizer migration, which was measured bycomparing the glass transition temperatures of each layer at an initialtime (t=0) and after the layers have achieved equilibrium. The resultsare summarized in Table 8, below.

TABLE 8 Net Plasticizer Migration and Properties of ExemplaryComparative and Disclosed Interlayers T_(g) at Δ T_(g) at t = 0Equilibrium Refractive (° C.) (° C.) ΔT_(g) (° C.) Index Inter- T_(g)T_(g) T_(g) T_(g) ΔT_(g) ΔT_(g) (Skin − layer Skin Core Skin Core SkinCore Core) Mottle CI-2 36 4.2 36 4.6 0.0 0.4 0.011 >5 DI-4 36 1.4 36.41.4 0.4 0.0 −0.005 <1 CI-7 42.5 2.2 42.5 1.4 0.0 −0.8 0.012 >5 DI-5 40.90.2 41.7 −1.8 0.8 −2.0 −0.004 <1

Disclosed Interlayer DI-4 exhibited minimal changes in the glasstransition temperature of both the skin and core layers of theinterlayer at equilibrium. This indicates a minor amount of plasticizermigration between the skin and core layers of each of Interlayers CI-2,CI-7, and DI-4. Although Comparative Interlayers CI-2 and CI-7 may berelatively stable, both exhibited a mottle value greater than 5, whichwould be unacceptable for most optical applications. In contrast, themottle value exhibited by Disclosed Interlayer DI-4 was less than 1.

The slight decrease in glass transition temperature exhibited byDisclosed Interlayer DI-5 at equilibrium indicated that a small amountof plasticizer migrated from the skin layer to the core layer. Suchmigration could be alleviated by utilizing a smaller amount ofplasticizer in the skin layer or a larger amount in the core. Even so,the refractive index of the core layer and the skin layer of DisclosedInterlayer DI-5 differed by only 0.004 and, as a result, the interlayeralso exhibited a mottle value less than 1.

Example 5: Blended Poly(Vinyl Acetal) Resins

Several Comparative and Disclosed Resins, prepared as described inExample 1 above, were mixed and melt-blended together with 38 phr of3GEH plasticizer to form Comparative Blended Layers CBL-16 and CBL-17and Disclosed Blended Layers DBL-27 and DBL-28. Comparative Resin LayerCL-2 is listed in Table CL-15 was formulated with Comparative ResinCR-10 and 38 phr of 3GEH, while Disclosed Resin Layers DL-27 and DL-28were formulated with Disclosed Resins DR-3 and DR-5, respectively, and38 phr of 3GEH. The haze and percent visual transmittance (T_(vis)) foreach blended resin interlayer were measured, along with the haze andpercent visual transmittance. The results are provided in Table 9,below.

TABLE 9 Haze and Percent Visual Transmittance of Several Resin Layersnposition Property CR-2 DR-3 Plasticizer (wt CR-10 (wt DR-5 content HazeInterlayer %) (wt %) %) (wt %) (phr) (%) % T_(vis) CL-2 100  — — — 380.5 87.7 CL-15 — 100 — — 38 0.5 87.8 CBL-16 96  4 — — 38 2.1 84.3 CBL-1789  11 — — 38 14.7 80.2 DBL-27 96 —  4 — 38 0.8 87.8 DBL-28 89 — —  1138 0.6 87.8 DL-27 — — 100 — 38 0.5 87.7 DL-28 — — — 100 38 0.5 87.8

As shown in Table 9 above, Comparative Blended Interlayers CBL-16 andCBL-17, which were formed from a blend of Comparative Resins CR-2 andCR-10, exhibited high haze values and lower percent visual transmittancethan single resin layers of Comparative Resin CR-2 (Comparative LayerCL-2) or CR-10 (Comparative Interlayer CL-15). In contrast, DisclosedBlended Interlayers DBL-27 and DBL-28, which were formed from a blend ofComparative Resin CR-2 and a high refractive index Disclosed Resin(Resin DR-3 in Layer DBL-27 or Resin DR-5 in Layer DBL-28), exhibitedsubstantially the same haze and percent visual transmittance asComparative Interlayer CL-2, which was formulated with Comparative ResinCR-2 alone. Thus, addition of inventive high refractive index resins toa comparative interlayer does not reduce the optical quality of theresulting interlayer.

Example 6: Preparation of Interlayers Having High Refractive IndexAdditives

Several poly(vinyl acetal) resins were prepared by acetalizing polyvinylalcohol with n-butyraldehyde. The resins, which had different residualhydroxyl contents, were melt blended with varying amounts of a 3GEHplasticizer and used to form various layers of multilayer interlayers.Each interlayer had an inner “core” layer having a thickness of 5 milssandwiched between two outer “skin” layers, each having a thickness of14 mils. The poly(vinyl butyral) resin used to form the core layers hada hydroxyl content of 11 weight percent and the resin used for the skinlayers had a hydroxyl content of 19 weight percent. Both resins had aresidual acetate content of about 2 weight percent.

Comparative Interlayers CI-17 through CI-19 were formed with resinlayers plasticized with 3GEH, which was present in varying amounts inthe core and skin layers. In addition to the 3GEH, Disclosed InterlayersDI-30 through DI-38 also included varying amounts of two different highrefractive index additives, Benzoflex™ 2-45 (diethyleneglycoldibenzoate; commercially available from Eastman Chemical Company,Kingsport, Tenn.) (Additive A-1), which had a melting point of 28° C.and a refractive index of 1.542; and Benzoflex™ 352 (1,4-cyclohexanedimethanol dibenzoate; commercially available from Eastman ChemicalCompany) (Additive A-2), which had a melting point of 118° C. and arefractive index of 1.554. The refractive index and glass transitiontemperatures of each of the layers of Comparative Interlayers CI-17through CI-19 and Disclosed Interlayers DI-30 through DI-38 weremeasured and the results are summarized in Table 10 below.

TABLE 10 Properties of Several Comparative and Disclosed InterlayersSkin Layers Core Layer Plasticizer High RI High RI Plasticizer High RI ΔRefractive Content Addi- Additive Total Content High RI Additive IndexInter- (P) tive (A) A + A:P T_(g) (P) Additive (A) Total A:P T_(g) (Skin− layer (phr) Type (phr) P Ratio RI (° C.) (phr) Type (phr) A + P RatioRI (° C.) Core) CI-17 40 — — — 1.476 30 65.0 — — — 1.467 2.9 0.008 CI-1840 — — — 1.476 30 75.0 — — — 1.466 −2.0 0.010 CI-19 40 — — — 1.476 3085.0 — — — 1.465 −3.1 0.011 DI-30 20 A-1 20 40 1.0 1.492 29 32.5 A-132.5 65 1.0 1.488 4.2 0.004 DI-31 20 A-1 20 40 1.0 1.492 29 37.5 A-137.5 75 1.0 1.488 −0.6 0.004 DI-32 20 A-1 20 40 1.0 1.489 29 42.5 A-142.5 85 1.0 1.488 −3.3 0.004 DI-33 17.2 A-1 22.8 40 1.3 1.496 30 22.8A-1 42.2 65 1.9 1.494 5.2 0.002 DI-34 17.2 A-1 22.8 40 1.3 1.496 30 26.2A-1 48.8 75 1.9 1.494 2.4 0.002 DI-35 17.2 A-1 22.8 40 1.3 1.496 30 29.8A-1 55.2 85 1.9 1.494 −2.1 0.002 DI-36 20 A-2 20 40 1.0 1.493 34 27.5A-2 27.5 55 1.0 1.490 15.9 0.003 DI-37 20 A-2 20 40 1.0 1.493 34 35.0A-2 35.0 70 1.0 1.490 8.4 0.003 DI-38 20 A-2 20 40 1.0 1.493 34 42.5 A-242.5 85 1.0 1.491 1.8 0.002

As shown in Table 10, above, increasing the plasticizer content of thecore layer of an interlayer that only included a 3GEH plasticizerreduced the glass transition temperature of the layer, which,ultimately, would have improved its acoustic performance. However, suchan increase also widened the difference between the refractive indicesof the skin and core layers, thereby reducing the optical quality of theinterlayer. As shown by comparison with Disclosed Interlayers DI-30through DI-38 in Table 10, the refractive index of core layersformulated with an additional high refractive index additive, remainedfairly constant with increased plasticizer loading, while stillexhibiting a similar reduction in glass transition temperature. Theresult was an interlayer having core and skin layers with nearly thesame refractive index, which greatly reduced optical defects such asmottle. At the same time, the core layer also exhibited a sufficientlylow glass transition temperature, indicating that the resin also hadacoustic properties.

Example 7: Preparation of Core Layers Having Reactive High RefractiveIndex Additives

Several resin layers, used to simulate the inner core layer of amultilayer interlayer, were formed by melt blending a polyvinyln-butyral resin having a residual hydroxyl content of 11 weight percentand a residual acetate content of about 2 weight percent with varyingamounts of 3GEH plasticizer. Comparative Layer CL-16 included 75 phr of3GEH, while Disclosed Layers DL-29 through DL-31 were formulated withvarious mixtures of 3GEH and a reactive high refractive index additive(reactive high RI additive). The reactive high RI additive used inDisclosed Layers DL-29 and DL-30 (Additive A) wasdiphenyldimethoxysilane (commercially available as SID4535.0 fromGelest, Inc., Morrisville, Pa.), and the reactive high RI additive usedin Disclosed Layer DL-31 (Additive B) was phthalic anhydride(commercially available from Sigma Aldrich Co., St. Louis, Mo.). Therefractive index of Comparative Layer CL-16 and each of Disclosed LayersDL-29 through DL-31 was measured and the results are provided in Table11, below.

TABLE 11 Refractive Index of Comparative and Disclosed Core Resin LayersPlasticizer Additive A Resin Content Content Additive B Refractive IndexLayer (phr) (phr) Content (phr) (nD25) CL-16 75 — — 1.466 DL-29 72 3 —1.468 DL-30 72 6 — 1.470 DL-31 72 — 3 1.470

As shown in Table 11, resin layers formed using 3GEH in combination withone or more reactive high refractive index additives had a higherrefractive index than resin layers formulated with only 3GEH. As aresult, when employed as an inner core layer in a multilayer interlayer,the Disclosed Layers DL-29 through DL-31 had a refractive index thatmore closely matched the refractive index of a skin layer formed ofpolyvinyl n-butyral (RI=1.477). As a result, multilayer interlayersformed with Disclosed Layers DL-29 through DL-31 as a core layer exhibitfewer optical defects than multilayer interlayers formed withComparative Layer CL-16 as an inner core layer.

Example 8: Various Interlayers with Resin Blends Having a HighRefractive Index Plasticizer

Two polyvinyl n-butyral resins, R-1 and R-2, were prepared according tothe procedure described above in Example 1. Resin R-1 had a residualhydroxyl content of 19 weight percent, while resin R-2 had a residualhydroxyl content of 11 weight percent. Both resins had residual acetatecontents of 2 weight percent. Several resin blends were prepared thatincluded varying amounts of resins R-1 and R-2 in order to simulatevarious blending rates. The blends were combined with 38 phr of aplasticizer selected from 3GEH (plasticizer P-1; RI=1.442), dioctylphthalate (plasticizer P-2; RI=1.485), a blend of 30 weight percent 3GEHand 70 weight percent Benzoflex® 2088, which is commercially availablefrom Eastman Chemical Company, Kingsport, Tenn., (plasticizer P-3;RI=1.506), and nonylphenyl tetraethylene glycol (plasticizer P-4;RI=1.500). The resulting plasticized resins were then formed into singlesheets that included both resins and the plasticizer. The refractiveindex, haze, and percent visual transmittance was determined for eachsheet and the results are provided in Table 12, below.

TABLE 12 Properties of Several Resin Blends Plasticizer P-1 PlasticizerP-2 Plasticizer P-3 Plasticizer P-4 Resin A Resin B RI of Haze T_(vis)RI of Haze T_(vis) RI of Haze T_(vis) RI of Haze T_(vis) (wt %) (wt %)Interlayer (%) (%) Interlayer (%) (%) Interlayer (%) (%) Interlayer (%)(%) 100 0 1.477 0.4 88.5 1.494 0.4 88.5 1.495 0.3 88.4 1.493 0.3 88.598.9 1.1 1.477 0.6 87.9 1.494 0.4 88.6 1.495 0.3 88.8 1.493 0.3 88.797.8 2.2 1.476 1.2 87.1 1.498 0.3 88.4 1.495 0.3 88.7 1.493 0.2 88.795.6 4.4 1.477 1.9 84.6 1.495 0.4 88.4 1.495 0.3 88.6 1.492 0.4 88.591.2 8.8 1.476 5.4 81.7 1.495 0.5 88.3 1.495 0.4 88.5 1.493 0.3 88.688.9 11.1 1.476 12.9 80.6 1.494 0.6 88.2 1.495 0.4 88.2 1.492 0.4 88.2

As shown in Table 12, above, although blended resin layers formulatedwith plasticizer P-1 maintained a substantially constant refractiveindex with increasing amounts of the lower hydroxyl content resin R-2,the optical properties of these resin blends having high levels of R-2worsened as the amount of R-2 increased. For example, as shown in Table12, the haze of blends that included more than 1.1 percent of resin R-2increased, while the percent visual transmittance of these blendsdecreased from 88.5 percent to 81.7 percent.

In contrast, the resin blends including more than 2.2 percent of resinR-2 that were plasticized with higher refractive index plasticizers P-2through P-4, each exhibited substantially the same haze value andpercent visual transmittance as blends having lower amounts of resinR-2. Therefore, it can be concluded that the resin blends utilizinghigher refractive index plasticizers, such as plasticizers P-2 throughP-4, may permit higher amounts of lower hydroxyl content resins withoutadversely impacting the optical properties of the final blend.

Example 9: Poly(Vinyl Butyral) Layers Including a High Refractive IndexPlasticizer

Several poly(vinyl n-butyral) layers were formed by combining and meltblending three different poly(vinyl n-butyral) resins (PVB-1 throughPVB-3) with different types and amounts of plasticizer. Each of theresins PVB-1 through PBV-3 had a different residual hydroxyl content,ranging from 11 to 20.4 weight percent, and all three resins had aresidual vinyl acetate content of 1 weight percent. Comparative LayersCL-17 through CL-19 were formulated with varying amounts of triethyleneglycol di-(2-ethylhexanoate) (“3GEH”; RI=1.442), while Disclosed LayersDL-32 through DL-37 included a mixture of 3GEH with Benzoflex™ 354(commercially available from Eastman Chemical Company, Kingsport,Tenn.)(RI=1.53). The refractive index of each layer was measured and theresults are summarized in Table 13, below.

TABLE 13 Several Poly(vinyl) Butyral Layers with Various PlasticizersPlasticizer Content Residual Ratio of hydroxyl 3GEH Benzoflex ™ 3GEH toTotal plasticizer Refractive Resin content content 354 Benzoflex ™content Index Layer (wt %) (phr) (phr) 354 (phr) (nD25) CL-17 19 38 — —38 1.477 CL-18 19 38 — — 38 1.477 CL-19 11 75 — — 38 1.466 DL-32 20.430.1 12.9 30/70 43 1.484 DL-33 20.4 25.8 17.2 40/60 43 1.485 DL-34 20.421.5 21.5 50/50 43 1.488 DL-35 11 59.5 25.5 30/70 85 1.479 DL-36 11 5134 40/60 85 1.481 DL-37 11 42.5 42.5 50/50 85 1.486

As shown in Table 13, above, resin layers that included a highrefractive index plasticizer exhibited a higher refractive index thanthose that included only a low refractive index plasticizer.

Example 10: Preparation of Interlayers Having High Refractive IndexAdditives

Several of the Comparative and Disclosed Interlayers formed in Example 9and summarized in Table 13, above, were used to create severalComparative and Disclosed Multilayer Interlayers. Each multilayerinterlayer included a pair of outer “skin” layers, each having athickness of 14 mils, sandwiching an inner “core” layer, having athickness of 5 mils, formed of a resin having a lower residual hydroxylcontent. The composition and several properties of the multilayerinterlayers, including total plasticizer content, refractive index,glass transition temperature, mottle, and loss factor, were measured asdescribed above, and the results for the Comparative MultilayerInterlayers CI-20 and CI-21 and Disclosed Multilayer Interlayers DI-39through DI-41 are summarized in Table 14, below.

TABLE 14 Properties of Several Comparative and Disclosed InterlayersTotal Δ plasticizer Refractive Refractive T_(g) Loss Interlayer SkinCore Skin content Index Index (° C.) Factor No Layer 1 Layer Layer 2(phr) (Skin − Core) (nD25) Skin Core Mottle at 20° C. CI-20 CL-17 CL-18CL-17 38 0.000 1.477 30 — 0 0.02 CI-21 CL-17 CL-19 CL-17 42.5 0.0111.475 35 3 5 0.32 DI-39 DL-32 DL-35 DL-32 48 0.005 1.484 38.8 2.6 0.40.41 DI-40 DL-33 DL-36 DL-33 48 0.004 1.486 39.6 4.7 0.4 0.39 DI-41DL-34 DL-37 DL-34 48 0.002 1.488 40.9 8.7 0.4 0.33

As shown in Table 14 above, interlayers formed from skin and core layershaving a refractive index difference greater than 0.010 exhibited moreoptical defects, as shown by the mottle value of 5. Additionally,Disclosed Interlayers DI-39 through DI-41, which utilized a highrefractive index plasticizer, exhibited a higher overall refractiveindex as compared to Comparative Interlayers CI-20 and CI-21, which onlyutilized a plasticizer having a refractive index less than 1.460.

While the invention has been disclosed in conjunction with a descriptionof certain embodiments, including those that are currently believed tobe the preferred embodiments, the detailed description is intended to beillustrative and should not be understood to limit the scope of thepresent disclosure. As would be understood by one of ordinary skill inthe art, embodiments other than those described in detail herein areencompassed by the present invention. Modifications and variations ofthe described embodiments may be made without departing from the spiritand scope of the invention

It will further be understood that any of the ranges, values, orcharacteristics given for any single component of the present disclosurecan be used interchangeably with any ranges, values or characteristicsgiven for any of the other components of the disclosure, wherecompatible, to form an embodiment having defined values for each of thecomponents, as given herein throughout. For example, an interlayer canbe formed comprising poly(vinyl butyral) having a residual hydroxylcontent in any of the ranges given in addition to comprising aplasticizers in any of the ranges given to form many permutations thatare within the scope of the present disclosure, but that would becumbersome to list. Further, ranges provided for a genus or a category,such as phthalates or benzoates, can also be applied to species withinthe genus or members of the category, such as dioctyl terephthalate,unless otherwise noted.

What is claimed is:
 1. A tapered interlayer comprising: a first resinlayer comprising a first poly(vinyl acetal) resin; a second resin layeradjacent said first resin layer and comprising a second poly(vinylacetal) resin; and a third resin layer comprising a third poly(vinylacetal) resin, wherein said first, second, and third resin layers areadjacent to one another; wherein at least one of said first, second andthird poly(vinyl acetal) resins comprises at least one RI balancingagent comprising moieties of a high RI aldehyde having refractive indexin the range of from 1.425 to 1.620, wherein the difference between theresidual hydroxyl content of said first resin and said second resin isat least 5 weight percent and the absolute value of the differencebetween the refractive index of said first resin layer and therefractive index of said second resin layer is less than 0.01, andwherein the difference between the residual hydroxyl content of saidsecond resin and said third resin is at least 5 weight percent and theabsolute value of the difference between the refractive index of saidsecond resin layer and the refractive index of said third resin layer isless than 0.01, wherein said interlayer comprises a tapered zone havinga wedge angle of at least 0.13 mrad.
 2. The tapered interlayer of claim1, wherein at least one of said first, second and third resin layers istapered.
 3. The tapered interlayer of claim 1, wherein at least two ofsaid first, second and third layers are tapered.
 4. The taperedinterlayer of claim 1, wherein all of said first, second and thirdlayers are tapered.
 5. The tapered interlayer of claim 1, wherein theouter two of said first, second, and third resin layers each have aglass transition temperature that exceeds the glass transitiontemperature of a middle one of said first, second, and third resinlayers by least 10° C.
 6. The tapered interlayer of claim 1, wherein themiddle one of said first, second, and third resin layers is tapered. 7.The tapered interlayer of claim 1, wherein all of said first, second,and third interlayers comprise said RI balancing agent.
 8. The taperedinterlayer of claim 1, wherein said wedge angle of said tapered zone isnot more than 1.2 mrad, wherein the difference between the maximum andminimum thicknesses of said tapered zone is in the range of 0.13 to 1.2mm, wherein the width of said tapered zone is at least 5 cm.
 9. Thetapered interlayer of claim 1, wherein the refractive index of at leastone of said first, second and/or third resin layers is at least 1.480.10. The tapered interlayer of claim 1, wherein at least one of saidfirst, second and third polv(vinvl acetal) resins further comprises a RIbalancing agent is selected from the group consisting of a solid RIadditive and a high RI plasticizer having a refractive index of at least1.460.
 11. The tapered interlayer of claim 10, wherein said RI balancingagent comprises a solid RI balancing agent present in said first resinlayer in an amount of at least 1 phr.
 12. The tapered interlayer ofclaim 1, wherein said RI balancing agent has a refractive index of atleast 1.450 and is present on said first poly(vinyl acetal) resin in anamount of at least 5 weight percent, based on the total weight ofaldehyde residues of said first poly(vinyl acetal) resin.
 13. Thetapered interlayer of claim 1, wherein said first resin layer furthercomprises at least one plasticizer having a refractive index of lessthan 1.455.
 14. A windshield comprising: a first glass layer, a secondglass layer, and the interlayer of claim 1, wherein said taperedinterlayer is positioned between said first and second glass layers. 15.A tapered interlayer comprising: a first resin layer comprising a firstpoly(vinyl acetal) resin having a first plasticizer, wherein therefractive index of said first resin layer is at least 1.480; a secondresin layer adjacent said first resin layer and comprising a secondpoly(vinyl acetal) resin having a second plasticizer; and a third resinlayer comprising a third poly(vinyl acetal) resin having a thirdplasticizer, wherein the refractive index of said third resin layer isat least 1.480, wherein said first, second, and third resin layers areadjacent to one another; wherein at least one of said first, second andthird poly(vinyl acetal) resins comprises at least one RI balancingagent comprising moieties of a high RI aldehyde having refractive indexin the range of from 1.425 to 1.620, wherein the difference between theplasticizer content of said first resin layer and said second resinlayer is at least 15 parts per hundred resin and the absolute value ofthe difference between the refractive index of said first resin layerand the refractive index of said second resin layer is less than 0.01,and wherein the difference between the plasticizer content of saidsecond resin layer and said third resin layer is at least 15 parts perhundred resin and the absolute value of the difference between therefractive index of said second resin layer and the refractive index ofsaid third resin layer is less than 0.01, wherein said interlayercomprises a tapered zone having a wedge angle of at least 0.13 mrad. 16.The tapered interlayer of claim 15, wherein the outer two of said first,second, and third resin layers each have a glass transition temperaturethat exceeds the glass transition temperature of a middle one of saidfirst, second, and third resin layers by least 10° C.
 17. The taperedinterlayer of claim 15, wherein the middle one of said first, second,and third resin layers is tapered.
 18. The tapered interlayer of claim15, wherein all of said first, second, and third interlayers comprisesaid RI balancing agent.
 19. The tapered interlayer of claim 15, whereinsaid first and third resin layers further comprise at least oneplasticizer having a refractive index of less than 1.455.
 20. Awindshield comprising: a first glass layer, a second glass layer, andthe interlayer of claim 15, wherein said tapered interlayer ispositioned between said first and second glass layers.